Which type of character are you creating for your story? Before you can answer, you need to know the differences.
When I hear the word villain, I think of an old-fashioned, cartoon baddy. Mustache-twirling. Skulking in the shadows. It can be hard to pull off a villain because they often come across as two-dimensional. But if I had to name a well-done villain, I’d say Voldemort from the Harry Potter books. He’s bigger than life (or death), he’s bad as all get out, and he’s got no redeeming qualities. Villain.
If you are writing an antagonist, you are writing a character that wants something that is in opposition to your protagonist. If you’re protagonist wants to save a historic building, your antagonist wants to tear it down. If you’re protagonist wants to win the heart of the cool boy, so does your antagonist.
Unlike a villain, your antagonist is not necessarily bad. He just wants something that is in opposition to your protagonist. They can’t both win.
In fact, your protagonist will probably be a more interesting character if he isn’t bad. Remember to give him some good qualities so that he is more well-rounded. Maybe he volunteers in a soup kitchen but thinks that the key to urban renewal is tearing down dilapidated buildings. Maybe she wants to date a specific boy because he is into the environment and so is she. Or he plays her favorite sport.
The fact is that it is really hard to make a bad-guy work if he has no redeeming qualities. I’m not really sure how Rowling managed to pull it off!