For me, Hands down Manta. Last time we went to Orlando in 2012, I rode Manta 7 times in one day. I was hoping for 10 but I ran out of time by the time we did everything else.
Honorable mentions go to Harry Potter's Forbidden Journey & Hulk. Although I haven't had a chance to ride it in Orlando, but if Transformers is anything like it is in California, then add Transformers to the list.