I have Project Fi, which is Google's phone service. It's $30 a month for the service and 1 GB of data. Which is a low amount compared to what other companies offer for the price, but I don't use that much data per month, and I get a credit back for what I don't use, making my bill per month even cheaper.
The service is great. Unless I'm in an absolute dead zone--which has only happened twice in the year that I've had the phone--I have great reception. I don't have to worry about being unable to call no matter where I am (even internationally) or getting online for information/maps.
Project Fi is great!
For those who don't know, Project Fi essentially works by placing you on one of three major carriers in the US based on who's got the best coverage at your given location. They're only partnered with T-Mobile, Sprint, and US Cellular at the moment, but I hope that can extend to more networks later down the road.
The only downside is that you have to activate your SIM on one of their designated phones, or else you can't use it. However, there's a "hack" that once the SIM is activated, you can insert the SIM into any unlocked phone, or so I've heard. 8)