Fire main always op even low lv ;P

Well sort of, although I think Earth main is pretty OP when it comes to some things such as 9 tails and mid game.

(I played earth main from L1 to around L65)

Although each main has its own pluses I would have to agree with you fire main is the most noob friendly =)

^Same with above^
I'd say go with OP firemains, or even lightning. Earth and water works best with some pains and rares and GNW ninjas

Go with fire for sure. Lightning pulls up at second best, but by the time you unlock the third skill in any class you'll already be close to being able to change the main character. Fire is best for low levels because of its variety, dps, and debuff usage/control. You could go the control route and debuff/sleep/seal the enemy to death, or just go damage in general. It's kinda squishy but whatever lol
Once you get to higher levels fire isn't necessarily the best, though

Earth is pretty squishy starting out until they get shields/immunity passive and later tier abilities.

till 60 Fire > Earth = Wind = Lightning > Water (unless you get GNW Kiba and iruka)

water main best main

I'd go with fire personally since he can do good damage in ninetail, which gives you more exp and coins as you get higher on the leaderboard.

Fire is one of the best pre and after lvl 60. I'd definitely go that route then change depending on who you pull.