Well, I thought the Junkyard Wars one was cool... And the one where you chose one click, where when your opponent killed it, you got the points. It was called Double Agent or something to the effect... And the first one I ever played was nice. Pick one of your opponent's clicks to use, and they pick one of yours, and you trade for the fight.
Though I'm not sure if my opinion still counts since I no longer actually really play or go to Hero HQ...