I love RCCL especially for the fun value. There's tons to do on the voyager or freedom class ships - voyager of the seas, adventure of the seas, or the freedom class - freedom of the seas, liberty of the seas.
The voyager class has tons to do and may be cheaper.
Carnival is usually a first-timer cruise company because it is one of the cheaper cruise lines.
Best of luck...and please get a travel agent with some experience.