T-mobile has been great so far. It's coverage is like 2.5x bigger than sprint's footprint. Data speeds for hspa+ "4g" are around 8-13 mb Download and 1-1.5 upload. Hspa is also technically 3g but on steroids so it doesn't use up lots of battery compared to true 4G (lte). Wimax is half of it's speeds but has barely any coverage. Sprint 3g gets butchered compared to this.
The data cap doesn't really bother me. 5gb is plenty of data for the average user unless they decide to watch Gangnam Style daily on it.
Now that sprint is bought by softbank I hope they can eventually get lte in the same areas as 3g soon because their lte finally lives up to standard. Tmobile deployed lte as well but they don't announce cities until they're fully complete.