It' s pretty cool that there doesn't seem to much of an issue with not having an extra memory slot.
Totally depends on the user's needs I must say. If you use your phone for entertainment purposes and play a lot of games, then the 32 GB will be your best bet.
I like keeping family, friends pics on my phone (However, I do keep a backup on my laptop), so the 16gb isn't sufficient for me. Besides that, the difference in price between the 16 and 32 gig models isn't that much.