In the last decade MetroPCS has gone from a small regional carrier to the fifth largest cellular network operator in the US. In 2010 they became the first carrier to offer a commercial 4G LTE network.
Pros: MetroPCS offers a variety of flat-rate plans that offer unlimited voice, messaging, and data options. Their LTE service means fast speeds where available.
Cons: While the company has expanded in the last few years, MetroPCS is still only available in certain regions of the country.