The disco at ROR is really, really fun. It is on the dim side because it is a disco and, you know, they don't make clubs bright. I still think it would be a great place for a reception. But, it only works for people that like to dance/party like that....people who just want to relax and take in scenery would probably rather be outside.
The disco will be private and you won't have onlookers/people not invited in your path. The other places will. I think if you have a dancing crowd the disco is a good choice, besides the beach doesn't close and you guys can always hang there after the disco. That's my 2 cents because we had a ball at the disco while at ROR. Great music too!