The seven major parks—the four Disney “kingdoms,” the two Universal parks, and SeaWorld—each warrant at least a single day to explore. Trying to cram more than one into your day will not only be stressful and unrewarding, it will also be a decision that your feet will never forgive you for. Given the price of admission to the parks, it’s best to get your money’s worth out of each individual park.
If you’ve only got a day or two and have never been to Walt Disney World [1], that should be where you focus your efforts. The Magic Kingdom [2] is an absolute must, and depending on the inclinations of your traveling companions, an additional day can be spent at your choice of any of the other kingdoms. If you’ve already been to the Magic Kingdom, any of the other Disney parks or either of the Universal parks [3] can easily provide a day or two of excitement.
For trips that will last 3–5 days, allow yourself a day at each of Universal’s parks, along with two days at Disney World and the remainder of your time checking out some of the lesser-known (and less expensive) attractions like Gatorland [4] or splurging on a day swimming with the dolphins at Discovery Cove [5].
If you’ve got a week or more in the area and a relatively fat wallet, I would still advise against trying to take in Disney [1], Universal [3], and SeaWorld [6] in one go. Instead, buy a multiday multipark pass from both Disney and Universal and alternate between them, taking time in between to check out some of what metropolitan Orlando [7] and the rest of Central Florida has to offer, or heading to the coast for a day or so at the beach. Unless you and your companions are absolutely crazy about theme parks, the area has a lot more to offer beyond thrill rides and fantasy.
Links:
[1] http://www.moon.com/destinations/florida/walt-disney-world-and-orlando-s-theme-parks/walt-disney-world
[2] http://www.moon.com/destinations/florida/walt-disney-world-and-orlando-s-theme-parks/walt-disney-world/magic-kingdom
[3] http://www.moon.com/destinations/florida/walt-disney-world-and-orlando-s-theme-parks/universal-orlando-resort
[4] http://www.moon.com/destinations/florida/walt-disney-world-and-orlando-s-theme-parks/other-nearby-attractions-0
[5] http://www.moon.com/destinations/florida/walt-disney-world-and-orlando-s-theme-parks/seaworld-orlando/discovery-cove
[6] http://www.moon.com/destinations/florida/walt-disney-world-and-orlando-s-theme-parks/seaworld-orlando/seaworld-adventure-park
[7] http://www.moon.com/destinations/florida/metro-orlando-and-central-florida