Get the nearest one to the park that you can afford. The first time we went we stayed at the Cheyenne (with 5 and 3 year old) - although there are loads of buses to the park it is were just too tiring to keep going back and forth. Second time we splashed out on the Disneyland Hotel and it was much better, we could walk back to the park several times a day, including last thing on an evening when there are no queues.
The best tip I can give you is take lots of snacks for your child as they are very expensive in the park - we took loads of crisps and cartons of juice, then took plenty of fruit from the hotel breakfast buffet. Also, check whether the hotel has tea and coffee making facilties - believe me you will need it as the park is very tiring.
I think your 4 year old will absolutely love it there, it's perfect for children of that age, and Florida will suit him/her better when he's older.