I would suggest Oklahoma or Texas. If you go to far west or to far east you add alot of travel time for those coming from the opposite coast. I know OK. is about 2 days (taking it easy) drive from the west. Any futher than that and I would have to take 6 days off just for travel. When considering a place to go we should also be thinking about what other group activities we want to do. Like race tracks, amusement parks, clubs/bars, sightseeing, beaches or special events going on in the area at that time.
While I'm at it I would also like to throw in Las Vegas as a spot to go. I know it is quite a drive for some, but there is alot to do here and most of the people on this board seem to be over 21 so the night life would be fun too.
My 2 cents.
Quincy