well i've been on NCL, Costa, royal caribbean, and carnvial.
i didn't pick NCL because i don't like the freestyle-ness of it. i like having the same waiter every night and getting to know them.
i didn't pick royal caribbean because i hate the curfew deal.
but i say a tie between carnival and costa.
i like carnival because they focus a lot on having fun and they have good food. and it's just a good time. and they have a lot of stuff for teens to do. plus the sushi bar every night was amazingggg =]
and costa because they have great food (i love the gelotto, sp?, every night). i'm italian so i gotta love it. there's a lot of international people on it which i think is cool. cuz i meet a lot of people from different countries. they didn't have the best teen program, and there weren't a lot of teens, but they didn't make a big deal about us. they don't check your age for the groups (i was 11 and went in the teen group..) you can stay out as long as you want. they don't kick you out of the disco. and the ones i've been on, it's mostly teens all night. they pour you champagne at dinner. you dance at dinner like every night. and the shows are good.
but yeaaaa.. there you go =]