Both depending on the place.

It's art obviously but it's a matter of where you create that art that makes it vandalism

Graffiti is art in a form itself. I really like the art style. I have done this type of art many times in my city in legal areas. When it turns to vandalism is when you do it on a owned wall or property, causing damage. For example Banksy in my opinion is not considered a vandal because he was doing it for a purpose. but if its some shitty throw-ups on owned property than yeah it is vandalism.

Graffiti is a kind of art. The location it is placed would decide whether or not it's vandalism.

It's artistic sure but the majority of the time is just abused.

It's both no matter how you look at it. You're destroying property but at the same time creating art.

It definitely depends on where it is done and the circumstances