For the best information on the cruise line, this is the place to post your questions and get great answers. I also like
www.castawayclub.com (great pictures) and you can get a quote straight from Disney at
www.disney.com (select Destinations and then cruiseline).
In 2000, we did the 3 day parks/4 day cruise on the Magic and thought we needed more time on the ship so this year (June 14) we're doing the 7 day eastern on the Magic with 3 days in the parks afterwards. My family has cruised on 4 other cruise lines including those to Alaska and Hawaii and we absolutely love the Disney ship. It lacks the gambling of the other ships, but that's no big deal to us. For most of our cruises, we've had kids of all ages with us and the kids really prefer the Disney ship as well. The rooms are bigger and the split baths in the majority of the cabins is an added bonus. We also get a verandah room on the Disney ship, something that isn't readily available on other ships.
I've never been on the Wonder so I can't comment on the difference between the ships but I have been on week long cruises before and that's the best way to go. I think doing a 3 day or 4 day is just to short to appreciate the ship. However, if your schedule only allows for a 3 or 4 day, take the 4.
Since kids are going with us and one of the other travelers is a teacher, we can only sail in the summer. We pick June because you can avoid huricanes.