Well, It's kind of complicated, so let me explain this as simply as I can. (BTW, I'm going to go through the Whole Story).
First, Venom was a Symbiote that attempted to possess Peter Parker as the Well-Known 'Black Suit' that Peter wore a few times. However, in realising what the Black Suit was doing to him, Peter rejected the Black Suit, and it came into possession of Eddie Brock, whereas it transformed into the so-called 'Venom'. At this point, Venom was a Supervillan.
However, as far as I know, Venom became an Agent when the Symbiote came into possession of Flash Thompson. Then is really when Venom became a sort-of good guy.
So I would think Venom as a Anti-Hero. He is not a Super-Good-Kind-Fly-Out-The-Window-And-Save-The-Damsel-In-Distress sort of hero, as he does kill people for even the Slightest Crimes, however, Spiderman and Venom both do have One Enemy in common, which is Carnage, in which Venom Hates because Carnage has no pride.
Too much information? Who Cares. I spent 7 minutes of my Whole Life writing that paragraph.