Well, for this we first have to consider the utility of each: fire is of course cool af, but what can you do everyday with it other than party tricks and crime? Maybe with some creative application you could like dampen your downwards acceleration or even give yourself a boost on inline skates or something that be kinda neat but I think it is still very gimmick-y. Water sounds in theory cool, since there is so much around you, you could keep yourself dry during rain, you could probably use it in the kitchen, you'd like never have to fear drowning anymore (as someone who can barely swim this is very appealing), and if you get real good at it maybe you can become a blood-bender and then shits real. Air has the usual flying stuff that's probably kinda cool and potentially useful for obvious reasons but probably not much outside of it? Maybe it can help with a breathable bubble underwater too? And earth... well you gonna make the sickest sand castles, but I fear it is similar to fire that a lot of uses for it are disruptive and violent.

I think I'd probably go for Water for the utility... although if fire includes lighting I might reconsider... although although blood bending is sick no fuck what, water it is