I just switched the other day from MetroPCS to the Boost Mobile MOTOKRZR K1m with the UNLTD plan. It's a pretty good deal and uses the Sprint network.
I have not bought into the whole cell phone thing yet. Actually I don't yap on the phone a lot anyway. So I use Tracphone for a cell phone. It's connected to the US cellular network here. It would be expensive if you talk a lot, but I don't. So Tracphone is very cheap for me. Beats any contract I would sign cause I never use very many minutes.
Yeah...in the more populated areas (city/immediate metro), the coverage is very similar in most cases. Once you get into the suburbs or more rural areas, you start to see differences. Sometimes those differences can be rather dramatic.