Meeting at a European city with a lot of routes from the US is a great idea. I didn't think of that.
Depending on all of the departure cities, though, may I suggest looking into Swiss to ZRH or Delta/KLM to AMS? I suggest those because they are probably the two easiest hubs in Europe to navigate and potentially sit around in. ZRH in particular is my favorite airport in the world. I actually like being there.