We have sailed
DCL, NCL, and
RCCL with our kids. RCCL is our teens' top choice hands down. Primarily due to Coco Cay (which was absolutely amazing), but also the Flow Riders, climbing wall, zip line, etc. DCL has basically nothing for active teens. NCL we were on a ship with a go kart but not much else and the pool decks were so crowded you could barely walk around, much less find chairs together. I am not bothered by drinking in general, love a good pina colada in the sun, but there was noticeably more drinking-as-a-primary-activity compared to other lines. NCL is also where my 18 year old son enjoyed sitting in the hot tub and met some some generous folks who shared their unlimited drink package and bought him several drinks. Not my favorite vacation memory and could have turned out much worse than it did.
Dining - On DCL we love the main restaurants and Palo (haven't tried Remy), except when we're stuck at a table crowded close to other tables which has only happened a few times. NCL we enjoyed the upcharge specialty restaurants but the main dining option was meh and truly dangerous with their cavalier approach to my son's food allergy. On RCCL we had the concierge dining and that was a blessing as it saved us from the main dining room which was horrible in atmosphere, food, and service (though to be fair we only gave it one chance). Breakfast and lunch buffets/quick dining were about the same on all 3 lines.
Service - NCL (not concierge) was a huge disappointment after sailing DCL (both concierge and non) so many times. For RCCL we booked concierge which was comparable to DCL concierge.
For future cruises with our late teens/young adults, we will absolutely choose RCCL and an itinerary that includes Coco Cay. No matter what line we're on, we typically plan for watersports at Caribbean ports and have several great memories of that, like hydroboarding (Grand Cayman), cliff jumping (Jamaica), river tubing (Jamaica), snorkeling with aqua scooters (St Kitts), waterslides (Nasssau - Atlantis), etc.