"Cool" is a relative term in Central Florida, since the winters are generally mild and this season has been relatively warm so far. However, temperatures in the 60s and 70s are a far cry from the 90+ degree summer days, and they make for a comfortable outdoor experience.
It's nice to see any of the parks in mild weather, but cool days are especially good for visiting animal-focused parks. You're more comfortable walking around, and the animals are more active when the temperatures aren't sweltering.
Here are the three parks that are perfect to see in the winter:
Busch Gardens Tampa: This park has vast outdoor animal habitats, with everything from cute little meerkats to majestic lions and speedy cheetahs. There are plenty of thrill rides, too, but on a cool day it's very relaxing to intersperse animal watching with rides on SheiKra, Montu, and Cheetah Hunt. After you ride their namesake coaster, you might even be lucky enough to see the live cheetahs sprint on a mild morning.
Busch Gardens Tampa has lush, lovely landscaping that you can appreciate more in the cool weather. The park offers extra-cost safaris, so you might even want to hop on a truck, head out to the Serengeti, and feed giraffes. The cool season means more animal activity and better viewing, so bring your camera.
SeaWorld Orlando: This park has underwater viewing areas for the dolphins and orcas and plenty to see outside, like flamingos, a shark pool, a stingray pool, seal lions, and the dolphin nursery. You can even buy food for many of the animals, like the sea lions, dolphins, sharks, and rays.
Like its sister part in Tampa, SeaWorld Orlando is beautifully landscaped, and winter offers perfect weather to stroll around and appreciate the plants and flowers. Its three main animal shows are held in outdoor stadiums, so cool temperatures mean a more comfortable experience. Just beware of the splash zones or you might end up soaked and shivering!
Disney's Animal Kingdom at Walt Disney World: This park is so lushly landscaped that it feels as hot as a jungle in the summer. In winter, the temperatures are perfect to really appreciate all the animal habitats worked into the park's pathways and the two main walking trails. Pagani Forest Exploration Trail features a troop of gorillas, while Maharaja Jungle Trek has resident tigers.
The animals on the trail and those you see on the safari ride are all more active in cooler weather. You'll have some great photo ops, and if you want an ultimate experience, you can sign up for Wild Africa Trek at Disney's Animal Kingdom. This experience takes you out on the savannah on foot, as well as on a private safari. You wear gear that can be hot and uncomfortable in the summer, but it winter it feels just fine.