Hi! I was wondering which company has the best cell service on campus.
Verizon or at&t or tmobile
Currently using tmobile and am wondering if I should change
Verizon works very well and AT&T barely works. I would go with Verizon.
This wasn’t one of the choices on your list, but my son is on US Cellular, and has not reported any problems.
Mine were at Bates, not Colby, but swore that, among friends, anything other than Verizon was iffy. Of course, that’s a different city, entirely, albeit not that far.
But Ironically, many of these services run on each others’ networks in remote or underserved areas. Either in part or wholly.
I am a colby student. Get Verizon
Yep, Verizon! We travel in that area of the state a good bit and it’s the best bet. It even works at our cabin in the mountains. 
https://www.t-mobile.com/coverage/coverage-map claims that T-Mobile has 4G LTE coverage on the Colby campus and nearby areas in Waterville, Maine.
Here are the coverage maps for Verizon, AT&T, and Sprint:
https://www.verizonwireless.com/featured/better-matters/?map=4glte#maps
https://www.att.com/maps/wireless-coverage.html
https://coverage.sprint.com/IMPACT.jsp
If you are looking at MVNOs (e.g. Google Fi, Page Plus, Boost, Total Wireless, TracFone, etc.), here is a list of what networks they actually use:
https://www.whistleout.com/CellPhones/Guides/which-network-is-your-mvno-on
^“Claims” is the key. I can tell you that Verizon is the best from talking to friends, but even its map is overgenerous in describing its coverage area. There are definitely coverage gaps on the route to our cabin that don’t show up on the map.