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.

You know what I mean. You pull up a Web page, and you decide to print it out for easier reading, or for filing. But you wind up with one or more wasted pages, usually at the very end, consisting of mostly blank space with just one line of useless text — perhaps just a copyright notice. Or, you waste a lot of ink printing images on the Web page that aren’t germane to the article.

There are ways to minimize this. You could use the “printer friendly” option on many Web sites. That may eliminate some unwanted graphics and text, but not all, and it doesn’t solve the problem of the wasted page at the end. Or, you can use a print preview feature, hope the preview is accurate, and then manually try to adjust the range of pages printed. But this doesn’t always work and it’s time consuming.

Now, a start-up company in Portland, Ore., has come up with a software product that aims to solve the wasted-page problem. It’s called GreenPrint, and it automatically detects these unnecessary pages and eliminates them from your printouts. The company, GreenPrint Technologies, promises that its simple software not only will save you money on paper and ink, but also will help the environment by saving trees — thus, the name.

GreenPrint inserts itself between your Web browser (or any other program that prints) and your printer. It takes the form of a faux printer. You print to this virtual printer, called GreenPrint, as if it were real. Then, it analyzes the document, identifies and eliminates wasted pages, and hands the document off to your actual printer, which prints it.

The product also has some other nice features. It can save any Web page as a PDF file, which can be called up later in the free Adobe Reader program. It can also show you a detailed preview of a Web page, or any other document you’re printing, and allow you to manually eliminate pages from the printout.

GreenPrint costs $25 after a 14-day free trial (it goes to $35 after the holidays) and works only on Windows XP and Windows 2000 for now. A Macintosh version is planned for next summer. It’s available from the company’s Web site, printgreener.com.

I tested GreenPrint on two Windows computers. Each was connected to my home printer, an H-P DeskJet 5850 model, which automatically prints on both sides of the page.

In my tests, GreenPrint worked well, correctly identifying and eliminating wasted pages and properly creating PDF copies of Web pages. I tried it with both the Firefox and Internet Explorer Web browsers, and also with Microsoft Word, for non-Web documents.

After you install GreenPrint, it adds two new entries to your list of printers. One, called GreenPrint, is the virtual printer you use to eliminate the extra pages. The other, called GreenPrint PDF, is used to directly save Web pages and other documents as PDF files. GreenPrint doesn’t erase your actual printer from the Windows printer list. You can still select your regular printer and bypass GreenPrint, but you won’t get the benefits of GreenPrint. In fact, while it makes sense to make GreenPrint your default printer, you don’t have to do so.

GreenPrint can work automatically in the background. But, if you want to make sure it’s only eliminating unimportant pages, or if you want the opportunity to cull the printout manually, you should use its preview feature. This presents a very nice print preview, better than the one in the new IE 7 browser.

If you double-click on any page in this preview, it turns red and won’t be printed. You can also right-click on any page to have GreenPrint eliminate images or text before printing. From this preview screen, you can also save the document as a PDF file.

You can tweak how GreenPrint works. For instance, you can specify how few lines of text a page must display before it’s considered worthy of elimination. Or you can add or subtract other factors GreenPrint uses to decide if printing a page would be a waste, such as whether a page has nothing but a border, or nothing but a single image.

If you want, you can set the program to analyze and eliminate only the final page in a document, or to only display its preview if it finds a wasted page.

There are some rough edges, however, and the product is something of a work in progress. At first, GreenPrint wouldn’t allow my printer to print on both sides of the paper. I asked the manufacturer about that and the company quickly sent me a new version of the product that fixed the problem. GreenPrint also crashed several times in my tests after I changed configuration settings. The company says a new version that avoids those crashes will be available for download by the time you read this.

Overall, GreenPrint is a good product — a simple solution to an annoying and wasteful problem.

Email me at mossberg@wsj.com.

These latest models aren’t quite as small as the teeniest laptops available, like Sony’s Vaio TX series, which are flaunted at airports like skinny fashion models at a photo shoot. But the new contenders have larger screens than the TX and cost less than the $2,300 or more that the Sony commands.

These new laptops all have screens that measure 12.1 inches diagonally. All hover around four pounds, though in some basic configurations some can weigh as little as three pounds. Even well equipped, they cost between $1,400 and $1,700.

Gateway began the most recent wave with a slender model released earlier this year, the NX100X, starting at just $1,400. But, unlike the Sony TX and other new models, it lacks an internal DVD drive.

I’ve been testing and comparing two newer entries that do pack an internal DVD drive into their small cases. One is the first ultraportable laptop from Hewlett-Packard in years, the Compaq nc2400. The other is one of the first crop of portables to be sold in the U.S. under the brand name of Lenovo, the Chinese computer giant, which now owns the IBM ThinkPad line of laptops. It’s called the Lenovo 3000 V100.

The H-P Compaq NC2400, already shipping, can be bought for as little as $1,549. A stripped-down model of the new Lenovo 3000 V100, which will be available soon, can be had for a mere $1,099. But the configurations of both computers I tested — selected and provided by the manufacturers — each cost precisely $1,649.

I like both of these machines, despite the fact that the H-P and Lenovo marketing people apparently skipped the class in business school about giving products simple, memorable names. You won’t go wrong with either of these laptops. But for their identical price, you get very different computers.

Based on “speeds and feeds,” the raw specs of a computer, the Lenovo offers much more than the H-P. But based on the key components of road-warrior mobility — weight, size and battery life — the H-P crushes the Lenovo.

Lenovo 3000 V100

The H-P is a dark-gray and black model that feels svelte, but solid. It is less than an inch thick, and the version I tested, with an extra-strength six-cell battery that protruded from the rear, weighed in at 3.8 pounds.

The Lenovo has a silvery lid and a black body that manages to look bulkier than it really is. It’s 1.25 inches thick, and the version I tested, which also had an extra-strength, six-cell battery that protruded from the rear, weighed 4.1 pounds.

The H-P also has a smaller footprint for a desktop or airline tray — 11.1 by 8.38 inches vs. 12 by 8.9 inches for the Lenovo.

I put the two contenders through my harsh battery test, where I turn off all power-saving features and keep the hard disk working.

The Lenovo’s battery lasted two hours, 41 minutes, an OK time for a little laptop. In more normal use with power saving on, it would likely approach 3.5 hours.

But the H-P Compaq nc2400 blew away the Lenovo on battery life, with a startling endurance of four hours, 27 minutes. This performance, one of the best I have ever recorded, suggests that with its power-saving features turned on, the little H-P could allow you to work for six hours straight without recharging.

On speeds and feeds, however, the tables are turned. The H-P I tested has a relatively wimpy Intel Core Solo processor running at 1.2 gigahertz, though it can be ordered with faster processors. The Lenovo has an Intel Core Duo, with the equivalent of two processors, running at two gigahertz. The H-P has 512 megabytes of memory; the Lenovo has one gigabyte — twice as much. The H-P has a 40 gigabyte hard disk. The Lenovo’s hard disk is 100 gigabytes.

I didn’t find the H-P sluggish at the typical, mainstream tasks I threw at it. But for the same price, you get much more power and storage in the Lenovo.

About the only basic spec where the H-P beats the Lenovo is screen resolution. The H-P’s is slightly higher — 1,280 by 800 compared with 1,200 by 800 on the Lenovo.

Both machines include built-in fingerprint readers, but the Lenovo also has a built-in camera, which the H-P lacks. The Lenovo also uses the same keyboard found on the ThinkPad line, which I regard as the best on any laptop.

The Lenovo lacks the rugged magnesium frame and hard disk shock-protection features that were pioneered on the ThinkPad. The H-P does have versions of these protective features. And the Lenovo uses a typical touch pad to control the cursor, while the H-P uses a mid-keyboard pointing stick.

With these two contenders, your $1,649 can either buy you a somewhat smaller machine with bare-bone specs but fabulous battery life, or a better-equipped model that’s a bit bigger and much more power-hungry.

Take your pick.

• Email me at mossberg@wsj.com.