We had a great experience at the Residence Inn Seaworld on our Christmas 2012 trip. You can click on the link in my signature for my trip report. It has lots of photos of the room, the common areas, and the pool/recreation areas.
The RI has free parking, free internet, and a free hot and cold breakfast buffet that's really quite good for an included perk. The RI also has suites with fully separate bedroom (or bedrooms, if you want two), multiple TV's in each suite, and a kitchen with a full sized fridge. The pool is zero entry (good for the little ones) and there's a large basketball/sport court in a lovely courtyard next to the pool and hot tub area.
Both the Doubletree and the RI will offer the same onsite benefits (free transportation, free QQ, etc.) and are very close to the SW parks.