Mostly, I'm with Wally.  First come-first served.  However, I'm rarely ever first-come.  I usually will still be paddling up until 7:00 PM or later before I really start looking for a site.  

No vote for me.  I'd be open to making all three choices depending on my own personal circumstances.  I wouldn't deliberately stiff a group from the only site that would work for them, though, unless it was also the only site that would work for me.