Don't waste your money on the 4S. Yes, it's noticeably faster but the screen is the same, RAM is the same, same design. You'll regret it. I like my 4S but if I had a 4, no way I'd upgrade.
The iPad 3 screen is pretty nice and double the RAM. But, the 2 isn't a slouch either. Bought my wife a refurb 2 and if I had to do it again I'm not sure I'd have bought my 3. Going from the 1, it's a huge difference and definitely faster. The 3 seems just slightly faster than the 2 with the screen being the only noticeable upgrade.