As always, this is a general guide aimed at mainstream, nontechnical consumers who dwell on common tasks such as email, instant messaging and surfing the Web; managing and lightly editing photos, videos and music; and using basic office applications. It is not intended for heavy gamers, video producers or corporate buyers.

There’s a vast variety of laptop models, but this guide is meant to cover the most common types of laptops, those with screens from about 12 inches to 17 inches, and weights ranging from around 2.5 pounds to 7 pounds.

For this column, I’m not including the category of tiny machines now called netbooks, with screens under 10 inches. I am also ignoring the huge, heavy laptops with screens larger than 17 inches that are primarily aimed at gamers.

Even the remaining mainstream machines range wildly in price, from bargain-basement models at $350 to high-end ones that can top $3,000. In my experience, the top brands for technology and reliability are Apple and Lenovo’s ThinkPad line, but various models from Sony, Hewlett-Packard, Toshiba and Dell are also worth investigating.

So, here is a quick guide to the key factors you should consider when buying a laptop.

Size: If you are a constant traveler, think about the subnotebook models, which generally weigh 3 pounds or less. There are two types of these. The classic subnotebook has a small screen, 12 inches or less, and a cramped keyboard. This year, a new type emerged, with a full keyboard and a normal 13.3-inch screen packed into a thin, light body. There are two of these: the MacBook Air from Apple and the Lenovo ThinkPad X300. All subnotebooks are relatively costly, typically ranging from $1,500 to over $3,000.

If your laptop will mostly stay at home, the office, or in class, a 5-7 pound machine with a screen of either 13.3 inches or 15.4 inches is the best bet. A well-equipped model in this class is likely to run you between $800 and $1,200. Typical models in this class are the Dell Inspiron 1525, the HP dv6700 and the Apple MacBook.

Windows vs. Mac: This is the eternal question. In my view, Apple’s Leopard operating system is faster, better and far less prone to malicious software than Microsoft’s Vista operating system. And the Mac laptops also come with better built-in software. The $1,099 MacBook is a solid, fairly priced machine, and the $1,999 MacBook Pro is even better. Both also can run Windows.

But Windows laptops are often less expensive, tend to have a greater variety of ports and slots, and come in more styles and sizes.

Apple’s MacBook

Operating system: If you are buying a Windows laptop, be aware that Vista is slower than Windows XP, in my experience, and still has compatibility issues with add-on hardware and software. If you’d prefer to stick with XP, you will find that many fewer models are available with it. And Microsoft has decreed that after June 30, mainstream, name-brand laptops will no longer come pre-equipped with XP.

Video: I recommend getting an LED-powered screen, which is brighter and saves power. Also, if you are choosing Vista, or if you do a lot of converting video for use on portable devices, consider getting a laptop with a separate video card inside that has its own memory.

Memory: If you’re buying an Apple laptop, two gigabytes of memory is plenty. If you’re using Vista Home Premium, I’d consider three gigabytes for best performance.

Processor: Any dual-core processor will be fine. Don’t pay a penny extra for faster processor speed.

Storage: In a mainstream laptop that will be your main computer, look for a 160-gigabyte hard disk or larger. A new kind of storage, called SSD, or solid state disk, is now available. But it is still way too costly for most users, and at the moment is available only in smaller capacities.

Battery life: Many laptops today rarely spend time away from an electrical outlet. But if yours will, look for a battery life of at least three hours between charges.

Wireless: Make sure your new laptop has the new, faster “N” version of Wi-Fi built in. Many cheaper laptops don’t. You can also get a cellphone modem built in, but they are costly and carry a monthly fee. You can always add an external cellphone modem later.

Other features: A built-in camera and microphone can be quite useful, and so can a feature on some Windows machines that allows you to play music and videos without fully booting up the computer.

Don’t let yourself be swayed by sales pitches, or by fanaticism for or against Windows or the Mac. Think hard about how you use your computer and what your budget will allow, and stick to those priorities.

• Email me at mossberg@wsj.com. Find all my columns and videos online, free, at the new All Things Digital Web site, http://walt.allthingsd.com.

But this isn’t the much-touted Apple MacBook Air, introduced last month with all those qualities. Instead, it’s a new ThinkPad from Lenovo, the X300. While the two machines are both impressive products, they are different in key respects.

I’ve been testing the ThinkPad X300 and I have found it to be a solid, innovative laptop that will be perfect for many mobile PC users. It isn’t as sexy or inexpensive as the MacBook Air, but it has numerous features the Apple lacks, especially a wide array of ports and connectivity options, a built-in DVD drive and a removable battery.

I can recommend the X300 for road warriors without hesitation, provided they can live with its two biggest downsides: a relatively paltry file-storage capacity and a hefty price tag. This ThinkPad starts at $2,476 for a stripped-down model and at $2,799 for a preconfigured retail version with a half-size battery. The configuration I expect to be the most popular, with a full-size battery and DVD drive, is about $3,000.

The key factor in both of these downsides is the solid-state drive, or SSD, which replaces the hard disk. The SSD is fast and rugged, but today it can hold only a cramped 64 gigabytes of files and is very costly. Apple offers a MacBook Air version with the same solid-state drive for a similar high price. But Apple also has a much more affordable $1,799 model with an 80-gigabyte standard hard disk. Lenovo doesn’t.

Lenovo’s ThinkPad X300

The X300, due to go on sale next week at lenovo.com and at a few retailers, isn’t as thin as the MacBook Air. In fact, at its thinnest point it is almost as thick as the Apple is at its thickest point. And when the new ThinkPad is ordered in what are likely to be its most common configurations, it is heavier than the three-pound Apple and, in fact, fails to make the three-pound cutoff that typically denotes a “subnotebook.” Only one configuration breaks that barrier, at 2.93 pounds, and it is the stripped-down model with just a half-size battery and no DVD drive.

But the X300, which will come with either Windows Vista or Windows XP, is still very thin and light. It’s under an inch thick and even at its heaviest is only 3.5 pounds. Yet, like the Apple, it packs in a widescreen 13.3-inch display and a full-width keyboard.

Plus, Lenovo has used that extra thickness to good advantage. While the MacBook Air’s extreme thinness makes it gorgeous, it left no room for an Ethernet jack, a removable battery, a built-in DVD drive or a cellphone modem. The X300 has all these things, either standard or as options, plus three USB ports, compared with just one for the Apple. The Lenovo even offers GPS location-finding, the ability to connect to new wireless USB devices and future support for a forthcoming wireless network standard called WiMax.

The ThinkPad has another advantage: Even though its screen is the same size as the Apple’s, it is higher resolution, so more material can be seen without scrolling. Some people find that higher-resolution screens make text too small to read easily, but I didn’t experience any such problem on the X300.

In my tests, the X300 performed very well, even though it has a relatively slow processor, slower than the MacBook’s.

But the ThinkPad’s battery life was only fair, and was inferior to the Apple’s. In my tough test, where I turn off all power-saving features, set the screen to maximum brightness, turn on Wi-Fi and run a repeating play list of music, the X300 lasted three hours and five minutes. That was 24 minutes less than the comparable MacBook Air. And this was on the $3,000 configuration with a full-size battery and a DVD drive. The more basic models, with a half-size battery, would last only half as long, according to Lenovo.

MacBook Air

In more normal use, the model I tested would likely last under four hours on a charge, and the base models maybe two, compared with about 4.5 hours for the Mac.

I also tested another version of the ThinkPad, which substitutes a second, half-size battery for the DVD drive. It got five hours and 15 minutes, which means you could likely get 6.5 to seven hours in normal usage. That model costs around $2,850.

There are two more factors worth mentioning. I believe that both the Mac operating system and the software that comes with it are superior to the Windows operating system and built-in software offered on the ThinkPad. And the Mac isn’t susceptible to the vast majority of viruses and spyware, and doesn’t require third-party security software.

Also, the ThinkPad’s screen, when opened, stands significantly higher than the Mac’s, so it is less usable in a coach seat on an airplane when the person in front of you reclines.

If you’re happy with Windows, can afford the price tag, and value the many ports and connectivity options Lenovo has packed in, the thin and rugged X300 is a great choice. It’s a notable engineering accomplishment.

Email me at mossberg@wsj.com. Find all my columns and videos online, free, at the new All Things Digital Web site, http://walt.allthingsd.com.

Most of the major specs I recommended two weeks ago in my annual spring guide to buying a computer hold true for laptops as well as desktops. That guide can be found at walt.allthingsd.com/guide. But buying a portable involves additional factors, so here are some tips for making laptop purchases.

First, you may want to wait to get that new laptop until later this year or early in 2008. There are a number of interesting new hardware features coming. One is called a “solid-state drive,” or SSD, which replaces the traditional hard disk with a faster drive made of memory chips like those used in digital cameras. Another is a “hybrid hard drive,” or HHD, which combines memory chips with a standard hard disk, for faster start-ups.

Also, more and more laptops will be using light-emitting diodes, or LEDs, to light up their screens — a method that promises to be both brighter and less power-hungry.

You also may want to wait for laptops with a new type of Wi-Fi wireless networking built-in. It’s called “N,” and promises to be faster and to have longer range.

For Windows Vista users, another new laptop feature coming soon is a small screen on the lid called a SideShow, which can display calendar appointments and new emails.

Even if you don’t wait, there are some features to know about that aren’t available on most desktops. One is a built-in Web camera and microphone, highly useful for making video calls and recording videos to be posted online. Another is a feature that allows you to play music, videos or DVDs without booting up Windows.

In addition, if you travel a lot, you may want something called a built-in WWAN, or Wireless Wide Area Network. This is essentially a cellphone modem that makes Internet connections over a cellular carrier.

Another key feature is a new kind of slot on the side of most laptops for add-on cards, like wireless modems. It’s called an ExpressCard slot and, confusingly, it comes in two sizes. Your old-style cards, called PC Cards, won’t fit in these new slots, so unless you want to buy new cards, you might look for a laptop that has both the old and new slots.

Battery life, weight and size remain crucial on laptops, unless you are buying a huge “desktop replacement” laptop, which will rarely leave the house or be unplugged. For everyone else, I recommend finding a laptop that offers at least three hours of battery life on a single charge, without requiring you to dim the screen so much you can’t see anything.

Most laptops cluster around the six-to-seven-pound range, which is fine for occasional travel, or for carrying between classes, or between home and office. But if you are a frequent air traveler and have the budget, shoot for a laptop that weighs four pounds or less and is small enough to use on a seat tray in coach even when the person in front of you reclines.

The most expensive laptops are at the extremes–huge, multimedia machines and ultra-portable models for hard-core road warriors. Most well-configured Windows laptops, with typical 15.4-inch screens, are between $900 and $1,500.

I find that laptops with 13.3-inch widescreen displays make a nice compromise between mobility and power. At the moment, there are very few brand-name models in that size, notably Apple’s $1,099 MacBook, which weighs 5.2 pounds; and Sony’s Vaio SZ line, which weighs 4.1 pounds but costs roughly twice as much. More 13.3-inch models are coming later this year from other manufacturers.

Finally, there’s the perennial issue of Windows versus Mac. Apple’s two laptop lines, the MacBook and MacBook Pro, are very good. They have better built-in software than any Windows laptop I’ve seen and don’t suffer from the security issues that plague Windows. And they can even run Windows software, if you need that.

But the Mac laptops lack some features that are common on Windows portables, such as slots for camera memory cards and built-in cellular modems. And the MacBook even lacks an ExpressCard or PC Card slot.

Among Windows machines, I think Sony and Lenovo make especially well-designed laptops, but almost any name brand would be fine.

Addendum: I’m happy to say there is a new, expanded and redesigned online home for all my columns. It’s at walt.allthingsd.com and access is free. It contains the current versions of the columns with the accompanying videos, plus a searchable two-year column archive and a new blog called Mossblog, which I will update occasionally.

This new column home page is part of a larger new Web site called All Things Digital, at allthingsd.com. In addition to my columns and blog, it contains technology news, analysis and opinion from journalists Kara Swisher, Katherine Boehret and John Paczkowski, and guest blogs from prominent technology figures.

My columns will still be published on The Journal’s main Web site, WSJ.com, which is available to paid subscribers and includes a much larger archive, going back more than a decade.

• Email me at mossberg@wsj.com