I'm comming from using AT&T's curve for a few months to now using Verizons Curve for almost a week now. Two Differences I've noticed:

1. Verizons Curve has Flash. So I can finally watch YouTube Videos on it. I couldn't do that with AT&T's curve (but you soon will be able too with the next update.)

2. Verizons Curve also records video. Not that I use this feature a lot, but AT&T's curve does not currently do this. This will also be added in the next update from RIM, so if you go with AT&T you'll have all these features soon.

I really switched to Verizon because I needed a phone that'll work everywhere, including the train tunnels here in DC, otherwise I would have waited for the update to be released on AT&T. Hopefully someone else will chime in with other features that I haven't noticed yet.

Hope that was helpfull.