Raptor @ Gardaland for me.
I don't go on coasters loads of times in a row (mostly because of queues), but I managed to ride Raptor about 8-9 times during the day. Several times in the morning, whilst everyone is getting into the park, once or twice in the afternoon and about 4 times after dark, where literally nobody is queueing for it!
Nemesis is probably my second, as it's such an amazing and forceful ride that never gets any queues.
And of course Kraken, I LOVE that ride! :--D ...which barely ever has a queue of over 45 mins...