My #1 son has iPad2, 64gb wifi/3G
I have iPad2, 32gb wifi/3G
Wife has iPad 3 with retina, 16 gb wifi only
#2 son has 'latest' iPad 3 with retina, 16 gb wifi - A6 processor and stupid new connector

Frankly, the only differences:

iPad 2 has better battery - if you get one, limited to 16 gb memory
iPad 3 retina has nice display, cellular LTE, and siri [which hardly ever works properly], and of course the large 128gb memory to store your entire life!

http://www.apple.com/ipad/compare/