Surfer: Could make a black hole to distract everyone while he exploited their weaknesses.
Firestorm: Could transmute everyone on the team imo.
Superman: Without cis, he would fly to the sun and amp himself before anyone noticed, wait for everyone to fight it out, and come back faster than anyone could react witha speed blitz.
I think that it would be between surfer and firestorm. Maybe.
It's not really a matter of experience, because you can easily turn your opponent into something fukked up. They're all capable of turning the players on the field into cotton candy.
Thor's hammer gives him some pretty impressive defense though.