The iPad is going to be the #1 tablet for a while. You cannot go wrong getting one. Just about every app that comes out does so on the iPad first. If you're not into Apple, then the only real Android choice in the 10"+ market is the Asus Transformer Prime. Nothing else comes close. The problem with Android though is there is no dedicated tablet app section. All you get is Editors Choice so if it isn't on that list good luck figuring out if the app has been optimized for tablets. 90% of Android apps are designed for the phone market so you'll have to get used to stretched/warped graphics, if it even works at all. Many phone apps just crash or hang on tablets. I know this because I own a Transformer Prime as well as an iPad.
If you want stability, choice of apps and true tablet optimization go with an iPad. If you want a lot of control of your tablet (folder, settings, etc) and don't mind fewer apps and sometimes flaky software performance, then get the Asus Transformer Prime. IMO those are the only premium choices out there right now. If you want a budget device, there's Kindle, the Nook or one of the other mid-sized tablets.