We have cruised with Disney & Carnival
If you are more interested in what the ship has to offer, then I suggest really looking at show ~vs~ show, pool areas - Do they offer adults only area with an adult only pool or just a couple of hot tubs, or just a bar area, also would the teenage enjoy slides or other water activities ~vs ~ only slides and such for the little kiddos. Do they offer movies, and what do they have going on during the day to enjoy as a family. If you have a rain or something if there something to keep you busy.
Dinning with Carnival I found the buffet to be just okay at times, it reminded me of Golden Corral / Sweet Tomatoes, not that there is anything wrong with either just my thoughts. I will say the pizza shop did have some really great pizza and other offerings. Carnival offers assigned dinner times or anytime dinning which you choose ahead of time when booking. We haven't done anytime dinning but will be doing it in Sept. When we are going with some friends to celebrate with them. I am planning to do a trip review after here on the DIS. As far as the food in the main dinning room, our last cruise with them was really hit or miss, with service and food quality. Overall we did not go hungry and did have some really good food.
As far as excursions go. We went in December of last year, and did the passion island inclusive which included lunch and adult beverages, or tea. The water was a bit cool, and quite a bit of sea weed. We had a really good time, food good and service was amazing, the beach and activities were fun. but get ready to tip, make sure to have some 5's on hand as getting change for a larger bills is not going to happen.