Most Helpful Guy
Plenty of men could nominate an ex wife or girlfriend... The best male villains (Hannibal Lecter, The Joker, Lex Luthor, Harry Lime, Magneto, John Doe in Se7en, John Kramer in Saw etc) are actually anti heroes. Despite them being the bad guys, we root for them. That's because they have extraordinary qualities that allow them to behave as we secretly sometimes wish to. So we admire their qualities and approvingly go along with their behaviour because it acts out desires that we are inhibited from expressing.
Catherine Tramell (Sharon Stone in Basic Instinct) is the only female example like this I can think of. Catwoman, possibly. I could include Nurse Ratched in One Flew Over The Cuckoo's Nest, but she's more of a realistic portrayal of a horrible horrible person, rather than a villain.1
Most Helpful Girl
That female terminator from Terminator 3 - Kristanna Loken. I remember watching the movie the first time with my two brothers when I was younger and wondered how someone gorgeous could be a villain lol.
And of course Harley Quinn is rather bad ass as well.0