Oblivion at Alton Towers, even back in 1998 when it was the onlyone of its kind. Such a long wait, such a lenghty hill climb, and then 11 seconds of ride.
It's a long time ago, so I'm not certain, but I think it would have to be the Corkscrew at Alton Towers back in 1980, the year it opened. I no doubt went on others at the time, but it's only Corkscrew I remember.