What size that you need will depend upon what you will be using the iPad for. What tends to take up the most space are films/tv shows and music - if you don't want to have many/any films/tv shows then you possibly don't need the 32 gig. But some of the capacity is already taken up by the operating system and built-in apps, so you won't have thefull 16 or 32 gig to play with, and the capacity can't be increased once you've bought it (though you can copy content off and on).
I would definitely say go for32gb, as I have a 16gb for the kids and they have almost filled it with apps alone. 16gb will fill up very quickly, you will only have about 14gb to start with as the iOS takes up 2 gb. If you are 1 of those that is not going to sync with iTunes much then definitely go for 32 gb as you will have to actively manage the storage on the 16 due to storage constraints. I bought the new iPad for myself in 32 gb, so glad I did instead of 16gb.
You can download a complete iPad User Guide here: http://manuals.info.apple.com/en/ipad_user_guide.pdf
Also, Good Instructions http://www.tcgeeks.com/how-to-use-ipad-2/
Apple - iPad - Guided Tours
Watch the videos see all the amazing iPad apps in action. Learn how to use FaceTime, Mail, Safari, Videos, Maps, iBooks, App Store, and more.
iPad How-Tos http://ipod.about.com/lr/ipad_how-tos/903396/1/
You can download this guide to your iPad.
iPad User Guide for iOS 5
What are all the differences between the iPad 3rd Gen and the iPad 2? Is the iPad 2 worth the cost savings?
What are all the differences between the iPad 3rd Gen models? Which should I buy?
Should I Buy a New iPad? Or an iPad 2?
A Few Questions (and Answers) About the New iPad
New iPad: A Polishing of the Old
iPad 1, 2 and New Specifications
How much content will fit on my iPod or iPhone?
If you think you may get an iPad 2:
Refurbished iPad Prices
New 16GB iPad 2 Prices