I have stayed at both OKW and Saratoga springs. They are both lovely resorts, but I prefer OKW for the following reasons: The rooms are larger than Saratoga Springs' rooms, you can park right in front of your villa at OKW (you mentioned having a car), the pool area is nicer, imo, and I love the "feel" of OKW---Keys-y, bright, and relaxed.
Both resorts have full kitchens in 1 br and up, both have washers and dryers, both are near Downtown Disney---Saratoga is just a short stroll away, and OKW just a boat ride (or longer stroll) away.
One potential minus for OKW---not all villa buildings have elevators.
Truly, I would be happy at either of them, but my first pick would be Old Key West.