21 Blast or Stun Mastery

From playing a Marauder, Blast is pretty decent damage with huge mobs. As for Stun Mastery, that's good if you're using Backspin Blow and Double-Upper a lot. I'd get Stun Mastery to a decent % or mastery-level, stop there, max Blast, then max Stun Mastery. I love doing this, btw:

BackSpin Blow -> (turn opposite direction) Double Upper -> (turn to opposite direction) dash forward and charge CorkScrew Punch at other mob -> (turn to opposite direction) BackSpin Blow -> (turn opposite direction) Double Upper -> and repeat!