Honestly, this is so fun! I'm still working on beating it at the moment, but here's an idea for some classes:
WIZARD
Ultimate + Passive: Singular straight blast
Primary: Spray for Blast
Secondary: Rapid Fire Blast
NECROMANCER (maybe an alternative wizard... or just unlocks in Endless after like 50 rounds of pain)
PASSIVE: Weak Beam
Primary: Revive 1 Fallen Enemy, have them fight for you
Secondary: Stronger Beam
Ultimate: Revive ALL fallen enemies from the round.
Rogue/Thief
Passive: Short Range spray blast
Primary: Stronger blast
Secondary: Hits in 2 directions, right and left
Ultimate: High range medium damage blast.
Let me know on how these are.