I need to put a vote in for
Google Project Fi. I got one of their phones about 8 months ago (Nexus 5x) and couldn't be happier. [Well, that's a lie, I can always find something to make me happier.] Their service for unlimited talk/text is $20/month, no contract. Data charges are $10 / gigabyte, if used. The big feature is that the phone automatically uses WiFi whenever it can find it. Call quality is excellent. I keep the "data" service turned off unless I really need it (and away from WiFi). So far, my total data charge for over 8 months has been under $3.