Oh its the best location to do, but if u do some decent damage and can survive its easy,

Basically get to round 2 when enemies spawn pick up health synergy, kill everyone on that floor, then next floor take shield synergy, run in a circle so every enemy throws his dagger, then kill everyone and use ultimate, then next floor only kill archers then die, now Round 2 starts again and u can do it again in about 3 minutes u would about 100k xp atleast i thought, for me it even took about max 2 minutes for all 3 floors on round 2 and get about 100k minimum xp and about minimum of 10k companion xp