Going to Apple's site, where it allows the user to pick a carrier or choose unlocked, they are all the same.

I thought all the major carrier did away with phone subsidies years ago so they could advertise lower monthly service fees, when those prices were becoming too high.

My phone is still subsidized, but it's through work, so I'm not the one paying the monthly bill. I didn't even think that was still an option for the average user buying on their own. Before switching my phone over to work, I had been buying unlocked phones at full price for a few years.