Which branch should I join?

As far as rank goes, with the Army unless you have a combat MOS, it comes at the same rate as Air Force. Combat MOS's will promote you much faster. I saw E-7 in 72 months.
Aviation in the Army is interesting. As an officer you will fly, but you are also placed into leadership roles. Most Army pilots are Warrant Officers to avoid the leadership path and continue to fly. Having said that, UAV pilots are enlisted in the Army where the Air Force requires officers to fly. In short, the Air Force is officer heavy.
I can very easily see how a AF officer would be QMP'd (Quality Management Program) when you have more chiefs than you have indians, things do get bad.
I wouldn't trade my Army time for anything, but I truly think, knowing what I know now, I'd been better off in the Air Force.