When are you visiting? Water parks have a rather large local presence, due to the relatively inexpensive water park annual pass. If FL is out of school, weekends get a lot of locals, and less out of state. But, weekdays will see less locals, and more out of state (taking a day off from the parks). Not sure you can predict which is better or worse.
If FL is in school (like end of Aug) then weekends are a lot less crowded than weekdays.
Edited to add: I would guess that the start of school makes weekend water park trips less enticing.