Gardaland: Basically the park I've visited the most as a kid (that still means only 1 visit every 2 years or so, so still not much) and I can't really recall which coaster have I done the most. It was probably Magic Mountain, since I've done it a lot as a kid or perhaps even Raptor, with my multiple re-rides on it in 2011. Can't really tell the exact number, but I think it's between 10-15.
Mirabilandia: Katun, 17 times (also the coaster I've re-ridden the most)
Europa Park: Schweizer Bobbahn, 3 times
Disneyland Paris: I didn't re-ride any of the rides due to lack of time
Busch Gardens Tampa: Kumba, 3 times
Santa Cruz Beach Boardwalk: Giant Dipper, 2 times
Universal Studios Hollywood: Revenge of the Mummy, 3 times
Six Flags Magic Mountain: Goliath, 2 times (again, lack of time to do more)
Wiener Prater: Super 8er Bahn, 3 times (I can explain...)
Tivoli Friheden: no re-rides, since all of the coasters there are crap
PBB: no re-rides, lack of time
Alton Towers: Again, no re-rides, due to lack of time
Thorpe Park: Swarm, Stealth, Saw and X, 2 times
Tripsdrill: G'sengte Sau, Mammut and Karacho, 4 times
Drievliet: Formule X, 3 times
Duinrell: Dragon Fly, 2 times
Walibi Holland: Goliath, 5 times
*note that I've listed the parks in order of my very first visit to each of them, if anybody's wondering