If you are having coverage issues with your current devices, assume the same with your iPhone when you get them. It won't do you any good to have two premium devices and not be able to enjoy them due to bad voice or cellular data reception. I've been with the 4 major carriers here in the U.S. and where I live and have lived, all 4 worked great. Having said that, I moved to Verizon because they have, in my experience, the best all around coverage. Still, that is not the case for everyone or in all areas. You have to make that determination based on your area. Once you've decided on who has the best coverage, go with that company and get your iPhones from them as well. That's my recommendation.