What's the best cell phone service provider?

I really depends on who has the signal were you want to use the phone.

If AT&T has a good signal and you don't travel overseas then Cricket might be a good option. or Ting if you have Sprint towers in your area. Now that Metro is part of t-mobile I have seen people using Metro pcs phone without having to go outside to find a signal. You Sprint phones might be able to port to Ting, if you have 6s or newer iphones or Pixel you likely can change to most companies if you have the phone unlocked. The new companies website likely has a page telling you which phones can be ported.

I think T-mobile might be the 2nd to Verizon now( and probably slightly less evil.)

I am currently using Google Fi and T-mobile. T-mobile has the benefit of offering phone insurance that covers loss and "unlimited" data plans. Fi has benefit of switching between Sprint, T-mobile, and Cellular one giving more coverage and if you go over data it doesn't cost as much as some other plans.

From most surveys Verizon is the best.

At the end of the day its a matter of which one you can afford to be with

we have AT&T and they are pretty good

According to Tom's hardware, T-Mobile is #2.

Probably Google FI if your phone is compatible. Otherwise AT&T or T-Mobile.