I think a human killing another human is more evil than a vampire killing a human. Most vampires (with some exceptions) kill humans for the blood, which they drink to stay strong and healthy. A human killing another human, however, is murder. Murder that doesn't help either of them in any way, whereas a vampire killing a human is usually so the vampire can feed.

Cuz vampires do it for a reason to eat (that doesn't make it right though)

Vampires have no choice. They have the hunger for their blood. Humans kill for envy, jealousy, greed or just for "fun".

Because they don't have to kill humans to survive as the Cullens have shown us, because humans are basically helpless against them, because Humans have a much shorter time as it is compared to Vampires in which to experience life without a vampire cutting it even shorter. To me it's like the difference between the murder of a child and that of an adult.

It's in the vampires nature to kill humans. They do it to survive yet what Vamp_Fan_25 said is true, it doesn't make it necessarily right. Unless they do what the Cullen's do and abstain from human blood, they can't really do anything about it and it's incredibly difficult to do what the Cullen's have done.

Human's have no reason to kill others. It's not necessary and the murder of a person by another usually reflects some kind of revenge/anger/jealously etc.