I have not been on Disney yet so I cannot compare the two lines but I have been on 4 RCI ships (Majesty, Monarch, Splendour, and Voyager). So far the Voyager was the one that I liked the best. It has tons of stuff to do on it and the Royal Promenade is, I think, it's best feature. We have always had an oceanview room and the Voyager and Splendour were the best as far as the rooms. We have not taken our kids on the RCI ships yet (Disney in Sept. will be their first cruise) so I can't comment on the kids programs. The thing I enjoyed about the Splendour was it is more intimate and relaxing, IMO. I hope this helps. Other than that, Cruise Critic's RCI board can give you alot more info.
Trisha