(Taz's) Texas Tornado at AstroWorld had a wicked first drop when it was at AstroWorld. I think they probably ruined it when they took it out west and shortened it, though.
Looks like the hypercoasters are gonna win this one 'cause they're all about the first drop. On that I'd go for the Big One at Blackpool. Especially when the tide is in!
Probably gonna get shouted down for saying it but I think the Vekoma Boomerangs have awesome first drops. The slow pull backwards is a real tension builder.
Apart from the obvious ones (Maverick! I could gush for days), I've always loved the front seat on Phantom's Revenge. Something about hanging practically vertical in the crook of the curve before the train fully crests makes it such a pleasant yet thrilling experience.