I didnt lose a battle with the following, but only averages 43 battles per key.

Gambler. Radiant/warlord
Bat. Labyrinth/cosmic
Beast. Eternity/cosmic
Wrath. Void/redemption. I also tried mark, hex .

I dont have banner or reaper, I would have tried those. A hiero was faster than bat, but had a few losses.

Put beast before wrath or it gets a bit more touch and go. I had wrath or beast die on occasions.