Guys, Guys. There is no end to the discussion on which operator is the best / provides best coverage.
1) This is largely dependent on Circles. As the circle varies, the coverage, customer support, and consistency varies. In fact, even the mobile internet speed varies.
2) This is again largely dependent on the areas you live, and frequently visit (for work / leisure / alternate home / etc.) At few places, the network is just terrible (Eg. inside houses). But that doesn't mean it is terrible in rest part of the city/state. A person who does not live / visit such areas would still claim that it is the "best" network in that state.
3) With the porting option, it is easy to switch to the network of your choice. This should be based on a short study conducted by you yourself for the areas which you would be for most of the time - this includes asking your peers who use other networks in that area.
4) Finally, from the cost perspective - I personally feel that lowest cost is better, but again this is my personal opinion only. There is no point in taking the lowest cost carrier if you dont get any signal in your house. Hence, choose wisely.