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But there's no shortage of rivals trying to dethrone the market champ, with most challengers to date relying on some variant of Google's Android operating system. Gartner predicts that 219 million tablets sold worldwide in 2016 will run Apple's operating system, compared with about 109 million for Android.

Google's own Nexus 7 (made by Asus) and Nexus 10 (made by Samsung) models lead the Android brigade and run the current flavor of Android called Jelly Bean. You still see some Android tablets running the previous version, Ice Cream Sandwich.

The Google Nexus 10 tablet offers a lot for the price tag.(Photo: Chris Thomas, Reviewed.com)

Specs-wise, the Nexus 10 boasts an even higher-resolution 10-inch display than the iPad, though you have a difficult time detecting much of a difference in a side-by-side comparison.

On the various Kindle Fire tablets that Amazon sells and the Nook tablets sold by Barnes & Noble, Android is present but shoved in the background and barely recognizable, replaced by those companies' own user interfaces.

A fresh challenge is coming from another flank, the radically different Windows 8 operating system driven by Microsoft and its PC partners. Windows 8 is designed not only for multi-touch tablets but traditional desktop PCs and laptops, a controversial and somewhat confusing decision for Microsoft that differs from the approach Apple is taking. Despite overlapping features, Apple is keeping the OS X operating system (for Macs) and iOS (for the iPad and iPhone) separate.

NPD data suggest a very slow start for Win 8 tablets so far, with market share of less than 1%.

The latest crop of tablets from all comers brings screen sizes that are typically in the 7- to 10-inch range, though you see some displays that are a bit smaller or larger. The trade-off to shoppers is obvious. Do you want more screen real estate? Or a lighter machine you might be able to stash in a pocket?

Apple's popular iPad has a 9.7-inch display; the recently added iPad Mini has a 7.9-inch screen.

Meanwhile, smartphone screens are in some instances expanding so greatly, that they are inhabiting territory occupied by smaller tablets. The Samsung Galaxy Note II, more phone than tablet despite the use of a souped-up S-Pen stylus, has been nicknamed a "phablet."

Prices are big and small, too, with most new tablets from well-known companies at a rough starting point of $200. Knockoffs from companies you've never heard cost even less, though they usually aren't as snappy or have screens that quite measure up.

At the other extreme, the current top of the line iPad commands $829, in addition to monthly fees you might incur for fast cellular data service.

Serving laptop masters

Tablets, of course, serve many masters. You use them to browse the Web, watch high-definition movies and TV shows, play games, chat over video, shoot pictures, catch up on e-mail, read books and periodicals, and otherwise entertain, educate and in some cases let you get work done.

The iPad excels in all of these areas. But rivals are making inroads and producing strong alternatives that are well worth considering, depending on how you're most likely to employ them:

• Tablets for readers. If reading is your passion, you have solid reasons to stick with dedicated eReaders, such as the various monochrome Kindle and Nook models from Amazon.com and Barnes & Noble, respectively, which some folks don't even consider to be tablets.

Electronic readers lack the color pizzazz of their multimedia siblings, but they're comparatively inexpensive, provide superb battery life and terrific glare-free screens, and they let you tap into enormous virtual bookstores.

Still, there's a reason that Amazon.com and Barnes & Noble are aggressively pushing the more versatile color tablets in their lineups. In many respects, the 7-inch $199 Kindle Fire HD, for example, is your entrée into Amazon's vast digital storefront. Collectively, Amazon offers more than 22 million movies, TV shows, songs, magazines and apps. On certain audio books from the company's Audible service, you can exploit a feature called Immersion Reading, in which text on the screen is highlighted while you hear professional narration. Another feature called Whispersync for Voice lets you read a Kindle book on the Fire and pick up where you left off on a corresponding audio book.

Amazon describes its X-ray for Books feature that is in the Fire as a way to "explore the bones of a book." It helps you find all mentions of characters, places and terms used in a book. A similar X Ray for Movies feature lets you peek at information about the actors in a scene you are watching culled from the Amazon-owned IMDb service.

Notwithstanding all the other things they can do, smaller-screen tablets such as Kindle Fire HD and Nook HD or HD+ generally work better for heavy-duty book readers than their large-screen brethren. It's also one of the reasons the iPad Mini ($329 on up) is arguably better for reading what Apple refers to as iBooks, than the full-size iPads — you don't mind that the Mini display, while perfectly fine, isn't as sweet as the full-size iPad's Retina display. Google's Nexus 7 ($199 on up) is also an excellent eBook reader. What's more, it's more than an eReader: It's a budget tablet that performs like a pricey machine.

It's worth pointing out, though, that Amazon, Barnes & Noble, Google and others make free apps available that will let you read their eBooks not only on those companies' own devices but on the iPad and other tablets as well.

• Tablets for business. A 2011 Forrester study found that of 10,000 information workers in 17 countries, 24% of workers in small businesses use a touch-screen tablet for work. While the iPad is primarily known as a play device, Apple has been pushing the tablet's business virtues. Apps can turn the iPad into a hub for capturing digital signatures, telephony and communications, and computer-aided design (among numerous other productive purposes).

But a chief drawback to using the iPad for work, and for that matter most touchscreen tablets, is the lack of a physical keyboard.

That's where many of the Windows 8 convertibles are trying to gain a competitive edge. They double as traditional laptops reliant on keyboards and mice, as well as touch tablets that rely on your fingers as the pointing device. The Lenovo Yoga 13, for example, is a $999 Windows 8 hybrid that via a 360-degree hinge can be contorted into four distinct modes: as laptop, stand, tent and yes, tablet. For all its PC-type virtues, which include an excellent screen and solid keyboard, however, it is a bit more clumsy to use in tablet mode.

Microsoft's magnesium Surface, starting at $499, is impressive hardware. It represents the first time Microsoft has built its own personal computer. Anyone wanting to use it for work, though, should seriously consider spending the extra $100 or so for a clever keyboard cover accessory that provides a very usable keyboard. It nicely complements the Windows 8 touch screen.

The confusing element here comes with the Windows 8 software. The first Surface tablets run a Windows 8 variant known as Windows RT, which relies on ARM processors and promises decent battery life. Surface RT comes with multitouch versions of Word, Excel and PowerPoint, but is overall short on apps. Worse, it can't run any of the legacy Windows software you've been using forever.

The Windows 8 Pro version of Surface that is coming in January will run those older programs, and it relies on generally more robust Intel processors. But it's heavier (2 pounds vs. 1.5 pounds) and, at $899, costs a lot more.

Meanwhile no matter which way you go, expect a learning curve as you get comfortable with the live interactive tiles that decorate the Windows 8 Start screen, a major departure from the Windows you grew up with. The traditional Start menu has gone AWOL, though some screens in this new Windows environment will look somewhat familiar under certain circumstances.

• Kids. There's a swell chance Junior wants to use your iPad, if not get one of his own — it's loaded with appealing games and apps for kids. Still, parents might instead want to consider tablets that were especially produced for the youngest members of the household. And a slew of companies are jumping into that playground, including venerable toymakers such as LeapFrog, Fisher-Price and Toys R Us, which produces the $150 Tabeo.

The $200 Nabi 2 tablet from Fuhu is representative of the category. It's a 7-inch, 1.3-pound Android tablet running off an NVIDIA quad-core processor. Housed in a red protective border, the tablet is preloaded with kids music, games and promises educational lessons tailored for K through 5 students. A Chore List app lets parents create tasks for their children ("be nice," "make new friends") and assign them rewards. Open the Web browser and you find buttons that take you to sites such as National Geographic Little Kids, Crayola Kids and Disney Fairies. Sites for grown-ups are kept off-limits. For $2.99 a month, you can stream kid-safe TV to the tablet.

The $150 Oregon Scientific Meep, also a 7-inch Android kids tablet, comes with a protective orange silicon bumper. It is targeted at 6-year-olds on up. Art and learning apps are preloaded, along with Angry Birds. Parents can tap into a cloud-based parental control portal without having to snatch the tablet away from their kids.

While a kid-specific tablet may be just what Mom and Dad ordered, Nooks, Kindles and iPads also come with built-in parental controls.

The iPad is clearly still the tablet to beat. But consumers have an increasing number of worthwhile tablets to choose from, with all sorts of sizes, prices and features.

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