Best villains imo:
Actually, Sensui bears some physical resemblance to Chrollo Lucifer (the guy with the black hair in my previous post), they're also from the same author
My list of best villains would have to be:
Because you're only badass when you do this to your opponent
Aaand, he cares about his comrades enough to massacre the mafia and plays a requiem along with it
(Although he can be a bit annoying XD).
Hisoka: SWAG, amazing personality and is always creative when he fights (being creative includes digging the meat of his chopped hand to take out a card to surprise the enemy
Phantom Troupe (Genei Ryodan): A really well-established villainous group, with amazing powers and personalities, they play both comical and serious without losing the group's villainous charm
Blue Beard from Fate/Zero was just awesome.
And while it's not from an anime, but from a game, Xehanort from Kingdom Hearts never ceased to amaze me as a villain