I ported over my first phone number about 6 years ago, and it's been receiving SMS codes without issue ever since. I'm not sure if that's increased the reliability of GV in general though since it still reports via Twilio's number lookup tool as a landline.

GV is great if you need to spend an extended period out of USA because cell carriers will drop your service if you they see you spending most of your time out of the country. When I spent a few years abroad, GV was pivotal for getting into banks account. Also really nice to be able to make outgoing calls via the web interface with a number you won't lose.