For what it's worth, I finally made a decision.
TL;DR version: T-mobile, and if coverage is an issue, I'll keep a Verizon Pay-as-you-go phone for backup.
Main objectives were to reduce costs, but also partially to stick it to Verizon who, despite offering good coverage, has provided nothing but a string of neutered phones and billing problems.
I put in 2 good years working with a T-Mobile partner, and heard nothing but good things about them. They also offer a very good discounted SIM only plan, with no contractual obligations. Cost is about $15/mo less than a 2-year contract with a discounted phone; enough that over the life of the contract. That's a pretty awesome deal, since the last time I bought a bundled phone was 5 years ago. It's enough to buy a shiny new Galaxy Nexus, but in my case, I'll probably find a good used Nexus S.
I'll see how T-Mobile coverage works for me. If it turns out to be an issue, Verizon offers a plan where I can pay $1.99 a day for unlimited usage, on-demand. There don't appear to be any monthly fees, and there are no minutes to expire.