I switched to Verizon / Visible not too long ago, and cellular coverage has been.. visibly better than Google Fi / T-Mobile. I mean I think that’s true everywhere but particularly outside of cities.
If I were to do it again (a few long distance trains at a time), Visible plus AT&T will probably cover all bases. Some people have a complex setup with Glinet routers with 5G and failover but when I’m out of network I just sleep or read (or play games)