The smartest move is just to get a 32--because the bigger the better--as they say. The more the merrier. And best of all, you're getting a beautiful phone and spending a lot on it, so I say go big or go home!!
(I went from an 8gb 2gen ipod touch to a 32GB iPod 4gen--amazing btw) and I have a lot more space now than before (obviously), but the point is that it just feels better knowing I spent 100 bucks more getting the 32GB iPhone rather than a 16....plus hopefully I can use my NE2 credit towards it, one, last, time lol.