Which one is best is tough. Which one has the most coverage is easy: Verizon.
But the complaints against Verizon are enough to scare me off.. READ THE FINE PRINT if you sign up with them.
My daughter just told them to bill-off (How's that for cleaning up what she really told 'em) As they kept increasing her monthly bill and reducing her features (Minutes, data limits) and Verizon is one of the companies that if you go over.. Well they may warn you (or not) it's a push notice to your device, but they also BILL YOU for the excess....... big time.......
I choose T-mobile. now at the time I was years from going on the road.. And they covered the limited area I traveled like a blanket.. My bill has NOT gone up, and my minutes and bytes have.. in fact... I went from 700 shared minutes, to 1000 to 1100 and finally UNLIMITED,, Messaging likewise has gone all the way up to UNLIMITED, and Bytes (Data) I get 6.5 GIG of high speed. (I used 6.2 last month the counter reset today, it was a "Big" month data wise) and if I go over.. NO EXTRA CHARGE.. Just slower speed (Dial up) which is good enough normally.
But they do not have nearly the high speed coverage.. They DO, however, have it where I need it.. So I'm happy.