Someone else here can probably answer better than I, but my experience on RC is that the people are very mixed. Lots of familes and a good amount of partiers too. I think you would have a good time. I would think the group varies by time of year and fare also. Spring break would be a good time for you, while August and the low price times like now you'll get people like me who are strapped for cash with my family. We're plenty nice and don't get in the way of anyone's fun, but the only thing I'm gettin is a stern look if I look your direction!
I hear Carnival is the "Party" line, but I choose RC because I'm a repeat traveler, and because they have the private island that Carnival does not and that makes ALL the difference for me.
Still, I think you'll do fine to try RC, I hear the food is better than Carnival and I noticed lots of good looking singles of both sexes having a good time.
Plus, the viking crown lounge (my favorite) is cool when they throw a party up there, on the Monarch and Sovereign it's really high up and has a cool view of the pool. My wife and I enjoyed that before we had kids. This time we have a son, so we'll just be happy to get a little bar time while the kid enjoys the Aquanauts program. I'll be the only one drinking however, as the wife is expecting our second.
Good luck and have fun!