It all depends on how you use your device. I personally always go for the largest storage because I need to keep movies, files, books, etc. on my device, in case I don't have wifi on my flights. If you're someone that manages most of their storage in the cloud & you don't keep a ton on your phone then 16 is fine. Again it depends on preference and how much you plan to store on your device.
Rumor has it the new iPhones will start at 32 gb. If true, you won't need worry about 16 gb. But if you have done well with a 16 gb, I don't see any reason why you can't continue that. You don't have to keep the profile. It's just for the beta.