I'm in the exact same position as you. I really liked the SGS2 . For what it seems you need it I would def go with the SGS2, most of my friends have it and it is a snappier than the cappy and the GPS seems to work much much better. In my opinion it is one of the best phones in ATT now. The skyrocket is good (but I dont have LTE in my city now) .
I would have gone with SGS2 but new phones are supposed to be around the corner (HTC X One and the mythological SGS3). I decided to flash ICS on my cappy (very smooth) to hold me out a few months.... Good luck tho. You cant go wrong w the SGS2