What is the definition of villain?
From a different point of view, Light would be the good guy, since he achieved, with questionable means, an enourmous feat:
he was able to make his world a better place, where criminality diminuished by ( if I remember correctly ) 90%. He didn't kill for his own gain, he killed for a better world. He became corrupted by his absolute power, and that was his downfall, yet one can sympathise with him, since he shouldered a responsibility so great all alone. No wonder he went mad.
Hisoka is imho not even a villain, he isn't evil, he doesn't want to destroy the world or such, he only wants to fight and kill the ones that catch his eye, at the point where he helps them if they're on a bind, like with Kuroro, and now with Gon. He is a bad guy, but by no means a great villain simply because imho he isn't even conceived as one:
he is a wild card, and does as he pleases.
Akainu on the other hand is ruthless on a level that his justice can't justify him:
he killed Ace, and that is were his justice ends. He didn't had any problem killing marines because they didn't want to die, you don't see Kizaru or Aokiji killing marines randomly, they fight against pirates because that's their job. Akainu on the other hand simply killed anyone that stood in his way of thinking. You don't see ppl hating Aokiji even if he almost killed all the crew, as well as many pirates in the war. Nor one hates Kizaru, when he did pretty much the same.