I pretty much stick to Aftermath and if I can't find what I want there, I'll play B2K.
Aftermath is an amazing expansion and is very well balanced, from a vehicle standpoint anyway.
The ONLY complaint I have about it is the same I have of everything BF3 in that inaccessible areas should be inaccessible regardless of whether or not a spawn beacon can be placed close and allow you to paradrop on top of it.
...it would be easy enough to do if they just considered these levels as out of bounds you'd be forced to get in bounds in 10 seconds or die.
The maps can become unbalanced if one good team is PTFO and the other is doing nothing. I don't know if it's so much a map design issue or just the ignorance of many BF3 n00b players and I don't know if it can ever be fixed?