All depends what you want from your holiday - or what you have already done on previous visits.
In 2000 we were in ASMo so we OD'd on Disney parks and water parks - only bought a 1 day sea world and 3 day Universal/IOA.
This year we're in I Drive so we've bought
5 Day Disney
14 day 5 park hopper (Universal/IOA/WetNWild/SeaWorld/Busch Gardens)
Also booked Discovery Cove - (But keeping that secret as it's a birthday surprise for the kids....)
Tony