I had a Verizon work phone for 20 years and ATT as my personal phone. Some places one worked, some places the other worked....like Yosemite. ATT worked better there.
Neither of the phone companies NEVER offer a plan without their best interest in mind. They always have some caveat that keeps the plan from fitting your every need. I think they spend a lot of time on research to make sure you never get a good deal.
ATT was offering a lot of gigs, but won't let you tether. I had an old ATT plan with unlimited data, but no tethering.
Recently, I had an issue with ATT where they were not even close to what Verizon was offering. I wanted out of country service (Canada) for 30 days. Verizon was something like $10.00 for 100 minutes. ATT was $5.00 for 100 text and some data, but a $1.00 a minute for calls. I could almost get satellite phone service for that. They refused to match the Verizon plan, even with threatening to change service. Finally, they gave me a $20.00 discount for three months. It's worth it to challenge and argue a little.