That's something you should knowI personally need 32gb but do you? Do you take a lot of pictures? Store videos, music etc on your phone? If so probably.. As I've said it's up to you
Since there's no removable storage I went for the 32Gb. It costs more, but for me it was more of a 'what if' factor, and that I wouldn't want to carry around an OTG cable and USB drive if I wanted more storage.