A to the data speeds, with all things being equal (signal levels, etc.), tmobile is faster than AT&T, but I have found AT&T's speeds to be quite sufficient. All will depend on phone, location, coverage. You will get the same as post-paid AT&T, so just ask your dad. With the limits, there is no known difference in the limit between the two networks. There is speculation that tmobile is more lenient, and gives more flexibility, but there has been no proof of that on a large scale. 2GB limit is the "safe" limit. Some have done more, and gotten away with it, but on the whole, this is the safe limit.