we love the key. If you are buying the internet anyways might as well get the key. The priority boarding, Chops Grille lunch on embarkation day, and priority disembarkation are worth the $. I have a teen who definitely gets the value out of the key times at the flowrider.
if you are familiar with a Beef on Weck you will be disappointed. I am from buffalo and also read about this sandwich. Huge disappointment compared to what I can get at a gas station here at home.
Agree with Matt, any Oasis class ship would be great. We have teens and usually get connected ocean view balcony staterooms. We just got off of allure and actually had 1 Oceanview balcony and 1 Boardwalk balcony across the hall. The kids loved the boardwalk balcony and its quite a bit cheaper (and came with free soda package for each kid).
San Juan, St Maarten, Labadee is the best itinerary. I just got off of Allure and visited these ports. With teenagers I think you should definitely stick to an Oasis class ship (Symphony, Harmony, Oasis, Allure)