I used to have T-Mobile 3 years ago. My description about the coverage? It is absolute garbage (I would like to use a different word... but you get the idea). You literally get what you pay for. In other words, you get bad coverage, which translates to bad data speeds (their so called 42mbps HSPA+ will never get that high. And the places that have it is very limited. Same goes with their 4G LTE network). Even their customer service got really bad over the year (used to be really good when I was still on contract with them. However, once the service went bad, I just paid the ETF and gave them the middle finger for the bad coverage and dropped calls.
Expect a lot of dropped calls and dead zones with T-Mobile. At least Verizon gives you what actually pay for (Good coverage and good data speeds). If you're so worried about money, then stick to Sprint or AT&T (more towards AT&T since Sprint has really bad data speeds and coverage isn't extremely fantastic). Hope this helped.