One of the perks of my past life in a sales gig was a company provided cell phone. So I've had all of the carriers at some point over the past 20 years. Nothing beats Verizon in my opinion. Even had coverage while driving through the big empty stretches of Nevada where the towns are 100 miles apart.
Doesn't help all of the time, but I've found that if you simply climb up to the top of the nearest hill, generally you can at least get a text out if you need to on many trails here in Arizona.
See my pics on Instagram @tucsonexplorer