It would depend on which part of Florida you are going to. If you are going to be in the Orlando-Kissimmee area there are the usual parks... Disney (all four parks), Universal Studios (and Islands of Adventure) and Sea World. This fall they will be opening the new Leggo Land where Cypress Gardens used to be. If you're going to be inTampa there is Busch Gardens and there is Silver Springs in Ocala. A safe bet is always Disney's Magic Kingdom, it's fun for all ages, if you haven't been, GO! Epcot is great for adults but not so much for kids. Disney's Hollywood Studios and Animal Kingdom are Ok too. If you're going when kids are out of school expect long lines and 75-80% humidity. Your best bet is to either go very early (get there when the parks open) or spend the day at the pool and have an early supper and go around 4:00 in the afternoon. The crowds tend to thin out a little and It does cool off nice in the evenings, plus you can stay for the fireworks. Also if you plan to eat in the parks you are better off getting the meal plan. It will save you about 30% otherwise pack another suitcase for food and souvenir money. If you are compelled to buy souvenirs and want to save some money. Go about 15 miles east of I-4 on hwy. 192 which is also Irlo Bronson Memorial Parkway and go to the Walmart next to Medieval Times dinner theatre. They actually have a great selection of Disney Licensed merchandise for a fraction of the cost inside the parks. That's about it, enjoy your trip!!
Oh, to pick a certain park would be difficult since it depends on how much you like Harry Potter and Disney. Also, during the summer, the parks will be crowded and warm. So, you may want to make sure you see the parks that have water rides like at the Jurassic Park section of Island of Adventure at Universal Studios. I attended the Grand Opening of the Wizarding World of Harry Potter which I thought was very nice.