Florida is very hot, and very, very humid from March to September, with the "worst" conditions being in the June/July/August period. Unless you are happy with very high humidity I would avoid these months, also this is the period of US & European school holidays, so there are a lot of people around, especially near any theme or water park attraction.
Like Sue, personally I would pick November, December or January, where temperatures will be just a bit above our summer.
Stuart
