Local to PDX, I think everybody has reasonable coverage. But once you get "out in the sticks", I find that Verizon is the only carrier with reliable coverage. (This is based strictly on my experience travelling about the PNW. I've got Verizon. I routinely travel with a group that has a wide sampling of carriers, and I'm usually the only one with signal on a reliable basis.)

AT&T and t mobile suck as for coverage. I did a 800 mile road trip through the south west and my iPhone was a brick, no service anywhere. As for my friend with the the same iPhone, but with Verizon had bars everywhere. It's worth the extra money for Verizon.

Had Sprint for around 10 years, hated the fact that I had to pay for 4G but never had 4G where I lived. Just switched over to T Mobile about 6 months ago and so far so good. I'm not on my phone much to talk so coverage isn't my main concern. Besides, I have wifi calling so it's not essential...as long as I have wifi (always at work or home, so yes). Data speeds are faster, and even though it doesn't work that well everywhere, it's working better than Sprint. Not to mention, their customer service through their Facebook ("T-Force") is pretty awesome. So far, so good.

Update: I switched over to T-Mobile for my business. The total plan was cheaper AND they have opened up Mexico and Canada for the plans. Travel there and just use the phones.

Picked up two new Samsung Galaxy S6 phones, switched over one Mifi, switched over my Gear S.

In the process, T-mobile has a deal going, get the S6 and get a Samsung Tab A, no charge! We do pay for the service.

Finally, the Phones are on the "jump" plan. Instead of upfront charge, we pay an on going fee and can switch out the phones, up to 3 times per year.

Cost is about $75 less per month.