AT&T it has the best coverage...I live in the middle of nowhere and no matter where I am and where i travel I always have service. My sister has AT&T and goes to the Nascar racetracks in several states and always has service no matter where she is even at the tracks she has service
Ive never heard of metro. I would say that for overall coverage either att or verizon will be your best bets. Verizon will run more but will give you the best coverage. ATT is decent but doesnt work well if you travel a lot.