iPhone 12 - differences between AT&T and Verizon models?

Hi - I’ll be getting a 12 Pro Max via Apple Upgrade Program, so I’ll be getting an unlocked phone either way. But I’m wondering if there are any even subtle differences between the models. In the past, I think they had different modems? I’m asking because I may end up switching carriers, and I’m not sure if I’ll have decided before I order my phone, so I want to know if it even matters. I know switching is possible either way, but I don’t know if it would be optimal.