T-Mobile has 50% more bandwidth than ATT, meaning faster speeds and downloads.  No carrier has 100% coverage, so you're always going to find somebody who's not happy with their coverage, regardless of who they're with.  My suggestion would be to look at their coverage map for your location and see if it's a good fit before purchasing: http://t-mobile-coverage.t-mobile.com/

All I know is that we have had t-mobile at home for the past 6 years.  Last upgrade we got unlimited data, and texting with 750 min of talk time a month.  I have used Verizon and AT&T at work and both stunk. 

Yup see the big black section between Rochester and Buffalo New York that's where I live lol no bueno.