Depends what your going for. I went from 2:73 to 3:55 and hated it. Lucky for me I dont drive it that much. The 2:73 just suited my driving style much better. If I had to do it again for a comfortable/ fun car thats not a race car, I'd go with the 3:27s. As for gas mileage, I cant help you out there. I did too many things at once and dont know what effected it, and how much on an individual basis.
3:55 = fun
3:27 = comfort
just my 2 cents, I'm sure there will be disagreements