In your situation for your combined usage, it sounds like CC would be a winner, but make sure you get the AT&T sim card and not the T-mobile sim. Your coverage will be better in most places. Both type of sims will start with 8901, but the next 4 numbers will be 4104 or 4102 for AT&T-based sims. If a T-mobile sim, the second 4 digits will be 2604 or 2609. These are based on my experience with att and t-mobile sims and their mvno's that I have seen. I have never actually seen a CC sim. I think the reason they are pushing T-mobile sims is that their wholesale cost is probably lower on the T-mobile network, meaning higher profit for CC.
On top of a better network using the AT&T sim, you should be able to take your current phones with you onto the CC network.
On top of a better network using the AT&T sim, you should be able to take your current phones with you onto the CC network.