I have used undercovertourist and mapleleaftickets both are good both have discounts some things are cheaper at each place depending on what you want to do. Ive only had undercover ship them to me but have been to the mapleleaf ticket office in Kissimmie.
never had a problem with either both are good places.
We use OnlineFlorida, in October instead of getting the Flexi plus ticket, we found we were able to buy two separate tickets cheaper that covered Universal, IOA, Seaworld, Aquatica and Busch Gardens all unlimited. The only park it didn't cover was Wet & Wild.