OK I'm and avid Disney fan, that being said if I were you I'd check out cruise ship reviews. I'm sorry I don't remember the web address but there is a web site that gives all sorts of ship facts for each ship, including what a ship was written up for the last time they were inspected. I've sailed on Carnavel and I would not do it again, but then everyone has a different idea of what is fun on a cruise.
No ship comes even close to the Disney kids program. Instead of a casino they devoted the space to a kids programs with different programs for different ages. They have a higher counslor to kid ratio than any other ship. There are adult only areas so parents are rested when they do get together with the kids and everyone is happier. There is also a track of kid/parent games and entertainment as well as a lounge just for families in the evenings. (The area of lounges etc. are adult only after a certain time in the evenings.)
As for price you are smart to start hunting early. You might try Vacatonstogo.com, or Allseas.com for a good price. Whatever you sail on I wish you a great trip.