It's been four years since Apple (AAPL -0.82%) unveiled the original iPad. Since then, the company has introduced more than half a dozen different models, while other manufacturers have flooded the space with tablets of all different shapes and sizes. With so many to chose from, finding the best tablets can be daunting. But among all the different options, a few stand out. Here are the best tablets on the market.

iPad Air
The successor to the original iPad, the 9.7-inch iPad Air is the overall best tablet on the market. It's light and thin, with great battery life and an insanely fast processor. At $499, It's expensive and doesn't offer expandable storage, but its app ecosystem gives it a huge advantage over its rivals.

There have been more apps written for the iPad than for any other tablet -- about half a million at this point, each one designed to look perfect on the iPad's screen. Whether it's gaming, entertainment or business -- if there's a mobile app for it, the iPad has it.

iPad Mini with Retina Display
The iPad Mini with Retina Display is everything the iPad Air is, just in a smaller form factor. The larger screen of the full-size iPad may be preferable for watching movies or typing out documents, but the Mini is obviously more portable, and easy to hold with one hand. It also costs $100 less.

Nexus 7
's (GOOGL 0.93%) Nexus 7 is a bit smaller than the iPad Mini, but far less expensive. At $229, it's almost half the price, while still offering comparable specs and a high-resolution screen. If you use an Android handset and have purchased a lot of content from Google Play (movies, books, games, apps), then it's an obvious choice.

The problem with Android tablets in general, however, is a lack of tablet-optimized apps. There are plenty of Android apps that were developed for smartphones, and they can all be used on the Nexus 7. But they're ugly -- in attempt to make them fit the larger screen, smartphone apps have to be scaled up, losing quality in the process. Google is taking steps to fix the problem, but for now, Android tablets still lag the iPad in terms of app optimization.

Galaxy Note 10.1
If the Nexus 7 is too small, then consider Samsung's Galaxy Note 10.1, the best large Android tablet currently on the market. Compared with the iPad Air, it's a tiny bit bigger and slightly heavier, but it has something that the iPad lacks: a stylus.

The Galaxy Note's S-Pen sets it apart from all of its competitors, letting owners write notes or draw with their tablet. And while you can buy a stylus and pair it with any other tablet, Samsung has put a lot of work into the S-Pen, with a number of dedicated software features including handwriting recognition -- it even works with third-party apps such as Twitter.

But that S-Pen will cost you: Starting at $549, it's actually more expensive than Apple's iPad Air.

Surface Pro 2
Windows tablets really haven't caught on -- perhaps it's the limitations of Windows 8, or the failure of Microsoft's (MSFT 0.22%) hardware partners to offer compelling products. At any rate, Windows tablets are hamstrung by their lack of apps -- the Windows App store is still a relative wilderness compared to Google Play or iTunes. But Windows tablets have their advantages. If you need your tablet to run full versions of classic Windows applications, there's no alternative to a Windows 8 tablet.

In that respect, the Surface Pro 2 is the best bet. Starting at $899, it's by far the most expensive tablet on this list, but Microsoft pitches it as a laptop replacement, and if that's what you're using for, it's not a bad deal. It's about as powerful as the average ultra-thin laptop, but it sports a full HD touchscreen and the body of a tablet.

There are cheaper Windows devices out there, but if you really want a tablet that can take advantage of the hybrid nature of Windows 8, the Surface Pro 2 is your best option.