Vegas is probably the best one because there still a lot to do outside the bash event. The hotel its hosted at is fine and the area around it has some cool stuff but its like 20 minutes from the strip, where all the real vegas action happens.
Last time I was there a lot of people at the bash went on a party bus to the strip to hang out at some of the hotel pools. it was pretty cool, and its a good wya to kind of mingle with people. These events get pretty cliquey and the worst part IMO is waiting alone at the party for people you know to arrive. The hot tub at the vegas bash is good for meeting people too because you dont have to yell to talk to anyone.
Anyone with a non-american accent at those events get a lot of attention though so if you sound pretty aussie meeting people should be easy