Apple set the de facto standard for modern tablets with its 9.7-inch iOS-powered iPad. With the right wireless keyboard and software, the iPad is effective as an e-book reader, note taker and basic office computing device. The recently rumored Microsoft Office for iOS might make the iPad an even better work tool.
Apple's newest full-size iPad boasts a more compact connector dubbed Lightning, and an A6 processor. Coupled with Apple's well-established app ecosystem and powered via iTunes, using an iPad as your main computing device is a very credible option, especially if all you're looking for is basic functionality. It plays audio well. It plays video well. It works fine as a gaming device as long you're not a fan of MMORPGs -- massively multiplayer online role-playing games -- in which case you'll need something with more punch.
For a tablet, the iPad is big and heavy. But compared to a notebook computer, it's light and easy to carry. Its communication options are top notch, including both Wi-Fi, and mobile broadband on multiple carriers. Add a good data plan if necessary, and you more than likely have all that most road warriors or students wishing to carry as little equipment as possible could need.
There are lots of hardware accessories available that make iPads more fun or useful. Unfortunately, the new Lightning connector doesn't work with most of the existing accessories out there, and replacement accessories for the new connector are only just beginning to arrive on the scene. Be patient and hardware companies should catch up eventually. Until then you can always buy an adapter cable for under $30 if you have old iPad accessories you'd like to use with the iPad 4.
The fourth-generation iPad is available directly from Apple or any number of online and brick and mortar retailers and ranges in price from $499 to $829 depending on storage and communications options.