I had T-Mobile and currently have Verizon. T-Mobile gave me better service around southern Maine (Saco-Biddo, Portland, Westbrook). T-Mobile was also better for me when I go up to Bangor or Eastport for work.

My wife had Straight Talk for a while and she almost always had better service than I did with either carrier. Especially when we were out towards Cornish and Fryeburg areas. I'd probably recommend Straight Talk or T-Mobile. Verizon sucks, and their customer service is equally shitty.