To determine whether Macbeth was a villain or a victim, it is necessary to establish whether he was responsible for his actions. He is described as a "tragic hero" which infers (suggests) that he is a noble man who has a "fatal flaw."
He is noble in battle which is why Duncan has rewarded him with Thane of Cawdor, due to his conquests. He does have a fatal flaw - his "vaulting ambition." So, at face value, Macbeth is more the victim than the villain.
Having established that he does meet the definition, it is necessary to consider Macbeth's position in context. Macbeth starts with the weird sisters (the witches). They foreshadow what is to follow and their mantra"fair is foul and foul is fair" will become a main theme in Macbeth and appearances will deceive as " "nothing is / But what it is not" (I.iii).
Macbeth himself is easily manipulated and, not only is he greatly affected by the witches and cannot decide whether they bode "good" or "ill," he is largely controlled by Lady Macbeth. Add this to his already ambitious nature and disaster is sure to be the result. Macbeth considers his position in Act I scene vii when it is obvious that he tries to persuade then dissuade himself. He is however, no match for Lady Macbeth who expects him to prove that he is a "man."
Macbeth does want to do it - he is ambitious after all- and whilst we sympathise with him because his wife has almost forced his hand and because the witches have had a huge effect on him, we see that he is villainous because it is being caught that scares him the most, not necessarily the deed itself.
Honor means a lot to Macbeth, as it would have done to all the men in the audience in Shakespeare's day. To be slighted and called a coward and to have your wife question your manliness would require you to prove yourself. It is as if Macbeth has no choice - "when you durst do it, then you were a man."(I.vii.). It is his misplaced belief in honor that prevents him from surrendering as he will not "shake with fear" (V.iii) and he is defeated at the end.
The choice between victim and villain then would be a personal choice. Perhaps he is both.