With those 3 parks as your priorities, and given the larger size of the alcove rooms, I would definitely go with the Dolphin. The location is so convenient, and the resort is very compact. You can walk to HS and Epcot so you can completely avoid buses and the skyliner lines if you choose to for those parks. The feature pool is really cool at CBR. I like the pool at Dolphin, but CBR is extra fun for kids, I think. You have so many food choices at Dolphin between the Dolphin, the Swan and all the Boardwalk area restaurants. We also always liked hopping into Epcot in the evening for food. I have never noticed the size of the beds at the Dolphin as being or seeming smaller. Doubles are of course smaller than queens, it just has never been noticeable for me when I am actually in the bed. I have stayed at the Swan (which has queen beds) and the Dolphin (doubles), and slightly prefer the Dolphin based on proximity to the larger pool, restaurants and other features.
Good luck with your choice!