To update: I called Best Buy to ask if VZ's model is CDMA and GSM, and was by a supposed person in the know (not the one who answered my call) told no, it's capable but not unlocked. And that the iPhone 4S wasn't either, although it was advertised that it was. Didn't sound right to me, so this morning I called VZ, and the person with whom I spoke confirmed that the new iPad and the iPhone 4S are indeed compatible on both CDMA and GSM abroad; they are unlocked. (The Verizon Wireless Web site also said that is the case, when I used their travel planner tool.) As others have commented elsewhere, the AT&T model has a removable SIM card, whereas the VZ model does not.
So, I can upgrade my 16G iPad1 3G with either the new iPad 4G (32G) with either VZ or AT&T or a used iPad 2 32G 3G with AT&T (the VZ iPad2 is not dual band). Would love some input from others!