My preference is Adults Only. I stayed at the Dreams Puerto Aventuras once before that was half adults only, but the adults side was boring, all of the action (dance lessons, activities etc.) were on the family side (and there were lots of kids splashing in the pool, etc). Yes some of the adults only resorts are full of honeymooners, but when we checked out the Excellence Riviera Cancun, it didn't seem that way at all. It was fairly quite, but not too quiet, and there seemed to be plenty of activities, and I just really like the fact that there were no kids around. Most of my guests are also really excited that the resort is Adults only. The Excellence is the resort that we picked.
Once you narrow down a location, I highly recommend doing a site visit of the resorts that you are inerested in. My fiancee and I spent one day touring about 6 different resorts (both adults only and family friendly). We really got a better sense for the resort once we actually toured it.