I'm usually using Finn lead (since forever), Sid, Lumi, Rey (6* now) and Poe. I started using Rey in arena at 4* with Finn lead as soon as I got her. Sometimes I swap Sid for Res Pilot, but it's not as reliable, and won't make me win against droid teams if I do this. I need the 1 AOE, and the 1 heal. Res units don't have AOE or heal :) I can live without those in some cases.
Wished I could get Trooper too, but I let him go when I farmed for Rey instead. Might get back to him eventually.
edit: Finn does a LOT more damage than Fives, especially on his first attack Crack Shot (65% bonus dmg on initial attack + his own buff on himself which is 22% offense). His expose/stun is fairly reliable as well (it works almost all the time, or or the other or both even). I never use his self-heal in arena. Unfortunately, the AI does, probably why Preemo said this is average on defense.
