So, here is my annual fall computer buyers’ guide, a simplified road map to the key decisions shoppers must make. I’ve focused on laptops—the most common purchase—but much of this advice also applies to desktops. As always, these tips are for average users doing the most common tasks. This advice doesn’t apply to businesses, to hard-core gamers, or to serious media producers.

Tablets vs. Laptops: If you’re looking for a light-duty, highly portable computer, it’s worth considering the iPad, which starts at $499, instead of a small laptop. This is especially true if you’re in the market for a secondary computer, or one mainly for use on the go. Many owners of iPads, including me, are finding it handily replaces a laptop for numerous tasks, such as Web browsing, email, social-networking, photos, video and music. It has superior battery life, lighter weight, and it starts instantly. I don’t recommend it for people who are creating long documents, especially spreadsheets and presentations, even though it is capable of those tasks. And I don’t recommend it for users who require, or prefer, a physical keyboard.

If you don’t like the iPad, there will soon be alternatives. For instance, Samsung’s Galaxy Tab, which has a 7-inch screen versus the iPad’s 10-inch display, and runs Google’s Android operating system, will be available this month from major wireless carriers. Sprint, for example, will offer it at $400 with a two-year contract. But some tablet buyers may want to wait till the first half of next year, when many more models will be available, and Apple will likely roll out the second-generation iPad.

Netbooks: These low-cost, low-powered little Windows computers are losing popularity, but are still available, typically for about $350 to $500. They are being hurt by the rise of tablets and by light but larger laptops. Some buyers also find the screens and keyboards are too cramped. But these are evolving. Some now have bigger screens and roomier keyboards. And Dell will soon introduce a sort of hybrid netbook-tablet. Called the Inspiron Duo, this model, starting at $499, has both a regular keyboard and a touch screen that flips around when the lid is closed to act like a tablet.

Windows vs. Mac: Windows laptops can be much less costly—and come in many more styles and varieties—than Mac laptops. The Macs start at $999, versus as little as $500 for a decently equipped Windows portable. Windows laptops are still dominant. But Apple laptops are stylish and reliable, and usually boot much faster than Windows machines, in my tests. Also, Apple scores high on surveys of customer support. Its latest models, like the new, light MacBook Airs, have extraordinarily good battery life. Macs also aren’t affected by the vast majority of malicious software, have much better built-in multimedia software and, at extra cost, can run Windows programs in cases where Mac equivalents aren’t available.

The light but speedy 13-inch Toshiba R705 offers good battery life.

Cost: Most of the popular consumer Windows laptops cost $500 to $800. You can get full-size laptops for as little as $280, but their processors and graphics are weak and some lack webcams. If you can afford it, a light but speedy 13-inch machine like the Toshiba R705 offers very good battery life for just under $800. All-in-one desktops typically cost around $1,000 and some, like the HP TouchSmart, offer touch screens with special touch software. Apple’s popular all-in-one iMac starts at $1,199.

Processors: The most promoted chips are Intel’s i3, i5, and i7 Core models, the latter two of which can turn on and off some of their functions to boost power or save energy. But there is nothing wrong with buying a PC that uses chips from rival AMD, which usually cost less. For average users, Intel’s older Core 2 Duo still works just fine, even with the latest software. Intel’s weaker Atom processor line powers most netbooks.

Graphics: Integrated graphics, which share the computer’s main memory, are fine for most common tasks, but costlier discrete graphics, which have dedicated memory, can speed things up by taking some of the load off the main processor. They also are better for games. Some computers have both and can switch among them.

Wireless: More and more laptops are coming with optional cellular modem chips in addition to Wi-Fi. These can be handy while traveling, but be warned that they require a cellular data contract, which can be costly.

Connections: If you plan to connect your laptop to a TV, look for a connector called an HDMI port, which is used on most high-definition TVs. Some laptops also come with a feature called Wireless Display, or Wi-Di, which, with an extra-cost adapter, can beam your laptop screen to a TV without a cable. There is a new, much faster USB port, called USB 3.0, but, so far, it’s on very few machines.

Memory: Aim for 4 gigabytes of memory, or RAM, on a new computer, and never settle for less than 2 gigabytes.

Hard disks: A 320 gigabyte hard disk should be the minimum on most PCs, though 250 gigabytes is OK if price is key, or if it’s your secondary machine. Solid-state disks, which lack moving parts and use flash memory like smartphones do, are faster and use less battery power. They cost much more, but are coming down in price fast. However, they typically offer much less capacity.

64-bit: Many models now use a 64-bit architecture, which allows properly written software to use more memory and run faster. If possible, buy 64-bit, which will become more and more important.

Touch: Some Windows 7 computers have touch capability built into the screen, though Windows wasn’t designed with touch as a core element and the combination isn’t ideal. Computer makers try to resolve this with special touch software, which you should try in a store. Apple laptops use huge touch pads as the multitouch surface, instead of the screen.

As always, don’t buy more machine than you need.

Find Walt Mossberg’s columns and videos online at the All Things Digital website, walt.allthingsd.com. Email him at mossberg@wsj.com.