In the book Frankenstein, there is no clear “bad guy”, the media made the Monster the original antagonist, but Victor created the monster. The Monster did kill everyone though, so it can truly go both ways, but who is worse?
Well Victor, he is at fault for the Monster killing everyone, because the Monster killed them in revenge for Victor leaving and not giving the Monster a partner so the Monster wouldn’t be alone. Victor did get warned if he didn’t make another creature the Monster would kill everyone Victor loved, so Victor promised the Creature he would make another, but Victor ended up breaking his promise and the Monster went to work. The Monster also warned Victor about marrying Elizabeth and Victor still continued to marry her and got her killed.
The Monster on the other hand was the killer, even if it was to get back at Victor, Killing innocent people for no good reason, is evil. The Monster was Reasonable, and it wasn’t like the Monster was asking Victor to kill his family himself though. The Monster was also the victim at first, new to this world and Victor just left him. Then on top that, Victor promised the Creature it would get its long awaited partner, and Victor breaks that promise.
In my opinion Victor is the bigger evil, not only for creating the Monster, But letting the monster murder him family when he could of done something about it. He could have listened to the Monster and Victor would have avoided all the murders, but he decided to be the hero at the wrong time.