As far as Oregon goes, I think maybe camp at Winchester bay and day camp to Florence and Coos Bay. All offer different riding and are worth visiting IMO.
Winchester has my vote if it's gonna come down to one of them, but I know plenty others like the trails a lot at Coos Bay. No beach riding at Winchester - not that you'd spend a lot of time there, but I'm sure people who never have wouldn't mind some time screwin around on the beach. Florence is a good mix (trails, decent dunes,beach riding), but doesn't really offer the 'best' of either.
St. A's is the one place I've never been to that I want to ride baaaaaaad. That should for sure be on the list !