Positive Role "Hero" or Negative Role "Villain"

An Actor who regularly plays a role of a hero if given the role of villain in a Movie or play he or she will find it hard to portray the Villain role.

Well the role of Amjad Khan as Gabbar singh was quit tuff compared to Amitabh bachchan and Dharmendra role as Jai and Viru in Indian Hindi Film Sholay.
 

A Good Actor find it easier and a lot more fun to play the villain. A hero is often very one dimensional but when you play the villain or negative character , you have many reign to make and modify the character your own and exaggerate it immensely you can add lot more sub-characteristics.

Also It depends on your personal liking. There are plenty of Actors who are villains only, but the key factor to play a hero or positive role is you enjoy being the morale of the film story, and at the end your character wins.

Negative character are more complicated. That doesn't mean they are difficult to play. They got more characteristics to them than the main hero. The film hero is all about good. But the villain can pretend to be good, but have bad intentions. It seems more difficult, but it doesn't have to be. It's something you have to be natural.