What's the best carrier to use?

I’m looking at getting a new phone soon, an upgrade from my iPhone 3G. I’ve chosen the Samsung Galaxy III but am still open to suggestions. But what I’m wondering is what carrier I should choose to get the best coverage and price planning. I need a decent data plan that includes unlimited text and a good amount of voice as well.

I’ve done a lot of research but am finding it a little hard to come to any conclusions. Any help that you all can offer is greatly appreciated.