I would have to say all of them. If you are gonna fly precision aerobatics, there is no control that is any more important than the others. Unless rolling, those wings have to remain level so precision on the ailerons is a must. On the elevator you must have precise control to nail those lines... 45's, verticals, hrizontals, wind correction, and 60's. The rudder is probably the most important...generally there is always some amount of crosswind, so to maintain your line, and track properly you have to have a precise rudder. The rudder is also important during rolls. You cannot be accurate if you are fighting the plane because the servos are not going where you command them. The recommendation to use the 8411's or appropriate digitals was a good one. Yes, they are more expensive. With that expense come higher performance, and reliability. JR has been the leader in servo development and technology for years, and the 8411 is just another example of that. I've seen the Hitecs before, and while I have seen them at meets work, I have also seen them put in a $10,000 FC Extra. Needless to say, that didn't impress me at all. I don't think I would take a chance on those personally. Can't say I've seen anything that eventful with the 8411's. I like flying...digging a $1500 engine out of the ground is not my idea of fun, but that's what happened in the case of the Extra above. You pay your money, you takes your chances, but my money will go on the good stuff.