said by toby:If you live in T-Mobile's 4G coverage area, they are the way to go, almost unlimited data.
ATT's has better coverage, slower HSPA+ speeds, limit the data to 1.5 GB per month.
Indeed, I live in ATT's strong coverage area, speeds are so so but consistent 4-6mbps down 1mbps up for the past 2yrs that I've had ST(Att sim).
Havent tried ST (tmo sim) but some folks I know have TMO and I know how iffy their coverage is, speeds a bit faster but not by much.
Similar to sprint has about the same or better TMO coverage but their speed sucks on certain devices, I know a friend with a Note 2 has blazing fast 10mbps-25mbps download speed.
Parents at home both have iPhone 4 and 4s with sprint & it has horrible web signal at home, but call signal is not an issue.