T-mobile is good-to-great in most medium and bigger towns. Coverage is also pretty solid as long as you're within a mile or two of an interstate highway. If you require wall-to-wall coverage, stick with Verizon or AT&T.
Ultimately, the best advice would be what was said above: get a T-mo SIM for yourself and use it on a test basis for a few weeks in the places you'd need coverage. Recognize that your temperamental colleagues will still find reasons to complain. Also perhaps they should get counseling for their anger management issues.