Pettigrew is a little bit complicated. He betrayed his friends, and this does make him a traitor, in my opinion. However, it seems that a lot of what he did was out of weakness and selfishness, and not really out of maliciousness, and he didn't appear to enjoy the life he had, working for Voldemort. There is the moment where he seemed to show Harry a bit of mercy at Malfoy Manor, when Harry reminded him that he spared his life. Pettigrew is not a good or sympathetic person, but I don't think I would consider him an evil person, either.