It really depends on what you like,
You say you like rollercoasters, then Busch Gardens is a definate.
There's also great rollercoasters at Universal Islands of Adventure, great rides (not necessarily rollercoasters, more themed rides) at Universal Studios. Seaworld also has great rollercoasters as well as all the shows etc.
If you like water parks there are loads, Wet n Wild, Disney has 2 waterparks, Seaworld has Aquatica etc.
Then you have all the Disney parks, Magic Kingdom, Animal Kingdom, Epcot & Hollywood Studios.
Other things to do, they have loads of Mini-Golf at different locations. Air boat rides, Gatorland, Shopping? Loads of Malls and Outlets.
If you're looking to go to the parks then you're probably looking at staying in Kissimmee, if you are then you're going to have a drive if you want a beach, although the Disney water parks have artificial ones.
If it's your first time and it's a one off kind of holiday then you're going to want to do as much as you can in case you don't go back, having said that I've been 4 times and done just about everything everytime lol.
My parents have a Villa out there so I'm kind of lucky