T-Mobile Simple One plan for $70 a month, total, including taxes and fees. Six or seven years ago, I have to admit that T-Mobile coverage wasn't that good. If my girlfriend and I drove the back roads in Napa Valley or some other location away from larger cities, I'd often have problems while she, who used Verizon, didn't.
But T-Mobile has been improving year by year, and right now I seldom have trouble with coverage and seldom have to rely on Wi-Fi in buildings or sports arenas.
One thing that's always been great is free data and cheap phone calls in most foreign countries. My girlfriend and I travel a lot, and the first time we went to Germany I could use my phone everywhere and she had to wait to get on Wi-Fil because she didn't want to pay Verizon for international data. She was so jealous.
So when we went to Egypt I put her on my plan for a month just so she could test it out. She loved it, and when we got back she switched from Version to T-Mobile. Since then we've been to Caribbean islands, South America, etc., and have had free data everywhere except Cuba.