In terms of freedom, T-Mobile was the only large carrier to oppose warrant-less wiretapping of Americans. In terms of cost, T-Mobile offered the best non-contract prices, and I could use my Nexus One or iPhone on their network for a reasonable price.
Me too, the even more plus plans from T-Mobile are great and most likely exist because of the parent company. T-Mobile also has great customer service and is my favorite US cellular provider. AT&T is worse in nearly every way except coverage area and now we'll have even less competition in the US, where prices are already too high.
