The Operating System
As the buyer of a tablet PC laptop you'll find you have two operating system options; Windows 7 and Android.
Android was designed from the ground up for smartphones, so it provides an interface that works perfectly with the touch interface of a tablet. Swiping your finger to move through programs and web pages is a cinch. However, Android has nothing at all in common with Windows, so using traditional Windows programs on a tablet PC laptop with Android is entirely out of the question.
Windows 7 is more familiar, of course, but it wasn't designed for a touch interface. Many of the buttons are small, which is fine if you have a mouse, but causes problems when Windows is used with bare fingers. Some Windows 7 tablets ship with a stylus as a result.
Ultimately, picking an operating system shouldn't be hard. If you want to use your tablet PC laptop for fun and games, or you want something that will be extremely portable and easy on battery life, go with Android. If you need a tablet PC laptop that's better suited for serious work, go with Windows 7.