We usually start at one park, do whatever we want to do their (we have been a bunch of times before, so there's always "tommorrow" of a line is long), then go back to the resort for a break or lunch. If we know there are a few things in a different park we want to do, we catch the resort bus back to that park, or go to the outlets or DTD, then go to another park for a nightime show. DH gets burnt out if we go to more than 2 parks in one day, but I would love to go to Epcot just to grab lunch or dinner. MK is my favorite, them MGM, but my stomach belongs to Epcot! It is a bit of time to wait for the WDW bus (10-15 minutes, usually) to go to another park, ride there, then wait on another entry line, but it is definetly worth it so you are not stuck in one park for the entire day (except MK, I could be stuck there 2 full days!)