hey ashley! i went on the galaxy (celebrity) in july, there were tons of teens (around 80), the counsellors were all supernice and we had our own disco! i met so many people and had a completely awesome time and i still talk to some people from the cruise!
I think any of the ships they've suggested so far are good, I've always loved carnival, basically any of the newer ships have awesome discos, the most importnat thing is the time of year that you go. Basically if you go during summer, most ships are going to have a lot more teens and younger people. So good luck with whichever cruise you choose