favourite villain damn that's a hard one for me since I have horrible memory XD
but well in manga I would have to say Friend from 20th century boy, the cult leader who has psychic god like powers that ends up controlling the strings of the whole world just to get to mars, the chimera ant king from Hunter x Hunter is a certified bastard XD, also and Honorable mention of the bastards of the "will" in Helck.
in comics (don't read much) but fucking Lucifer morning-star in sandman is the best Lucifer period, no discussion, no debate and you are wrong if you don't agree and you should feel bad.
form the W-C's Hannah from "A Better Place", girl you ain't no god, you ain't no devil, you are a petulant and dumb child who played with fire and now it's time for you too get burned.
from the world of anime I have to give it to the bastard of Beelzemon, selling his soul to the devil for power and killing one of the best characters while turning another one into a catatonic mess(god digimon 3 was dark man XD), also mentioning the bastards that are the anti spiral race from giant dick reference tengen toppa gurren lagann.
from the world of cartoons I give it to the lost dark soul of Ebon from static shock (wished they made a rebut of this one) and to the smooth one eyed mother F'err of Slade from the OG TT
and in movies I would give it to mister always forgotten, even though he played everybody like they where a fucking fiddle, Zemo from Captain A the 3rd. also Honorable mention to the glorious mother fucker of Killmonger (if I don't mention him people I know will have my head man D= ) and the crazy bitch from inception is what I would call an american yandere >XC (keep her away from me)