In terms of pure mathematical and economic value:
16 GB > 64 GB > 32 GB
However, value is subjective... so this is all nonsense.
Pick what you need, OP. If you have 18 GB of media and you don't want to have to switch which media you want on your iPhone all the time, then go with the higher storage capacity.
On the other hand, if you have barely any music or videos, go for the least storage capacity. I would still get 16 GB 4S over 8 GB iPhone 4, but the point is to get what you need.
I went with 64 GB for a couple of reasons. One; I've had 32 GB on iPhone 3GS and 4 for a while, and while it's enough space, it's just enough space. I usually have 31/32 GB filled (which is really more like 28/29 GB... damn storage gimmicks...). So, I'd like to give myself a bit more wiggle-room, especially since 1080p recording will eat up space very quickly.
Something else to consider is that if you resell your phone later, the storage will factor into how much you get. Usually, you can get a lot more for the most premium model, so that's what I decided to do in the end since I know I'll end up selling it for next year's revision.