Mini isn't too powerful, you just need to know how to deal with it. That's where the advanced movement system comes into play. You need to be dodging and getting out of the way of the mini. 2k4 is like an elegant ballet. Control of your player is just as, if not more important than control of your weapon. If you play this game like just about any other fps out there you're going to lose hard.
If you don't want to put that kind of time in to learn the game, then I'd suggest ONS. Fragging isn't as important in that mode, and having the vehicles to get you around the map alleviates the need to learn movement to some extent. You'll still need to learn the particulars of that mode though. That'll take some time, and you have to remember that you're playing against people that have been playing since release.