[QUOTE=Dagger]Good choices! I also love Hunter x Hunter's villains, particularly Kuroro. However, I don't know that I would call Hisoka a pure bad guy, per se; in my mind, he kind of exemplifies the "pseudo-evil" type of character one often finds in anime. In the later OVAs, he [spoiler]even plays on Gon's side in that volleyball game. And in the TV show's Celestial Tower arc, he ended up being the driving force behind Gon's improvement & determination--more like a straightforward rival than the usual shounen villain who must be defeated.[/spoiler] Basically, he gets in the way a lot, and he can be pretty ruthless, but I don't think he's a true antagonist on the same level as Kuroro & the Spiders.
~Dagger~[/QUOTE]
You are right--- Hisoka is more of a personal rival than an antagonist.
That's what I like about HxH. Although most of the good guys are moral, there is no ultimate villain to defeat (until the Spider Arc). In the Hunter Exam, even the good guys use sneaky techniques to defeat each other. In fact, one of the main characters (my favorite :D ) is an assassin. It's very much like Yu Yu Hakusho-- the good guys are often ruthless and 'cool', not pure or motivated by justice.
I also think that Illumi, Killua's brother, is a decent villain. He is creepy, murderous, and oppressive.
Just about any of the Spiders is a good villain. Feitan is good, as are Machi, Nobunaga, Ubogin, and Shizuku.