For me, it was about opportunity and choice. I was upgrade eligible with my AT&T plan, and at the same time, my mother had a vacant line on her Verizon fam plan that I snatched up. Picked up Verizon 32GB white 5 on launch day, then decided to pick up AT&T white 16GB 5 about a week later via Apple Store reserve system.
Upon comparing phones, the AT&T phone was in perfect shape, except the Home button felt slightly "squishier," and the Sleep button was slightly more recessed into bezel, and the left edge of the top glass back inlay was not completely flush with the back (was very obvious with a skin on). The front glass also didn't seem as tightly flush with the bezel at the top, and the screen looked a deep purple tint with polarized shades on (mucho importante inconvenience to me!).
My launch Verizon phone, on the other hand, had a minuscule "dent" or "chip" on upper right front corner of chamfer, and the back Apple logo had a horizontal line running across. Here's the desirable part about it: Home button was tight, screen looked normal with polarized shades on!!, and front glass was comparably more flush with bezel at top (as in, you couldn't stick a paper between it). I also liked having a factory unlocked phone out of the box!
Didn't want to return either phone, so I sold the AT&T phone for $850, stuck with AT&T plan because of unlimited plan and 1000 texts (both grandfathered). And I'd do it all over again if I could. Sent from my iPhone 5.