IN the vid, the last guys slider is sharp as an f'in razor, goddamn. Help that he was throwin some mid 90's heat too.
In the MLB, In terms of sheer movement/velocity(Nastiness) with no regard to control or placement, I think AJ Burnett has an unparraleled knack for making baseballs move in absolutely filthy manners. But he doesn't control it that great.
In terms of most effective breaking balls which calls for a mix between nastiness and control, I think Mo's cutter and LIdges Slider are in a league of their own. Mo throws his 90% of the time, and Lidge throws his 60+%, and could throw it more if not for his good fastball.