Teens are all different, but I'll tell you my experience. We recently cruised with two 17 year old boys, one ours and one a guest exchange student from Hungary (living with us for a year). Both boys really enjoyed the trip. I made them check out CG the first night, but it didn't appeal to them, so they didn't go back. My exchange student enjoyed talking to all the Hungarian CM's and even toured Nassau with one of them on her day off. My own son enjoyed exploring the ship on his own, and also touring Nassua with his dad. They both said they would definitely like to go again some day.
I think they would both have benefitted from having a close friend come along, but that wasn't feasible this time. Also, 17 years old is a little awkward - possibly too old for CG, and too young for a lot of the adult stuff. We did take them to Palo's (they are both well behaved and well dressed!) and they enjoyed that.
If your 14 and 17 year old like to be together, they will have a great time. If they are outgoing and want to meet other teens, they will have a great time. If they like a little peace and quiet and finding a place for themselves, they will have a great time.
Have fun!