Not saying you don't know this, but a ton of people don't understand this.
In terms of coverage, there are only 3 that you can choose from - Verizon, AT&T, T Mobile - everybody else (well really 4, US Cellular has its own also but they aren't nationwide)
Everybody else is an MVNO, they buy from one of the other 3.
The real question to look at when choosing is how is there data prioritized on the network. Most of the MVNO's data priority is the lowest you get, what that means is that when its a congested network, your service will be the worst of anybody. That happens pretty rare though, unless you are in a big city, in a big event space, etc.
this is a great resource to check to see how each MVNO gets prioritized data. Pick what main provider you want, then price shop the MVNO's on that network that have better prioritized data (if that is something you care about). If not, buy the cheapest one you can find on that service provider as they will all preform the same. Spectrum from what I read lost prioritized data about a year ago or so. I look this stuff up fairly often since I switch carriers for prioritized data. I'm not a fan of spectrum since they require you to have their internet, so they lock you so they can screw you somewhere else.