I am getting 16GB and no regrets (offcourse I can use more space).
My most space eating activity is camera/photos - so I sync pretty much everyday and move photos from Phone to iPhoto.
I had 32 GB - what I noticed was at the time of resale there is not much of difference between 16GB and 32GB - and given that apple releases phone each year - no point in investing in 32GB and sale it to price similar to 16GB
YMMV :-D