League: Depends on what's going on, but 90% of the time it's been the RoboRule since I've acquired it. Unfortunately I haven't been able to find enough head oil to keep it in my hands longer than a game and a half.
Tournaments: I usually start with the Havoc to read the lanes, and then go up or down from there. If it's reading the conditions well, I stay with that ball. If I need a stronger piece, I move to the Diablo or RoboRule, if I need something weaker, the VP2 or Panic...
Matt