I will be staying with at&t. The data speeds on at&t are great, and I have only minor coverage issues. The only times I've ever dropped a call has been when switching from 3G to EDGE or between at&t and a ROAMing tower, all things which make sense to anyone knowing how the technology works (heck, it takes almost a full minute to switch from LTE to CDMA or HSPA with existing LTE phones and infrastructure). I like being able to use my data while on a call (something you won't be able to do with a VZW iPhone, due to EV-DO's limitations) and I like getting coverage in cinderblock buildings.
I spent several years traveling between Seattle and Detroit by the various highway routes, and while doing testing for a former employer, I found that at&t had the most consistent coverage. It was the only provider to have coverage at the continental divide, on both I-90 and I-80. I was able to use my iPhone to stream a radio show from Portland, over EDGE, to my radio through some of the emptiest places in the US, and I wouldn't trade it for VZW's shotty network.
TEG
I spent several years traveling between Seattle and Detroit by the various highway routes, and while doing testing for a former employer, I found that at&t had the most consistent coverage. It was the only provider to have coverage at the continental divide, on both I-90 and I-80. I was able to use my iPhone to stream a radio show from Portland, over EDGE, to my radio through some of the emptiest places in the US, and I wouldn't trade it for VZW's shotty network.
TEG