Regardless of what ship you go on, the partying is pretty much up to the individual. Some singles groups are more party hardy, but there are other activities to particpate in as well.
For example, on our summer group most of the folks are anywhere from mid-30's to mid-50's and so far none of them are looking to go on this cruise and get smashed all of the time. Instead they are looking to have fun and meet new people with similar interests.
Most singles cruises will have fun activities to participate in as a group, so there are other things to do other than just party.
We have sailed a number of different cruise lines and like anything else, sometimes it is just a matter of what you make it.
Good luck and have lots of fun!