The creature is more human than Frankenstein because he takes complete responsibility for his actions, respects life more than Frankenstein, which is apparent by Frankenstein robbing graves to create the creature, and the fact that Frankenstein abandons the creature to die, only for the creature to experience the hatred of mankind which in turn teaches the creature to become a vengeful being and thereby causing the deaths of William, Justine, Clerval, and Elizabeth.
Another argument that can be made is that the creature reveals more human emotions than Frankenstein; for instance, in the beginning of the creature's life he is loving, benevolent, and passionate; he desperately desires companionship; something that Frankenstein lacks. Although the creature seeks revenge, it is quite apparent that he is a victim of abuse by his creator and society who ultimately drive him to his vengeful state. And it cannot be overlooked that the creature is able to express his feelings more freely than Frankenstein can.
Frankenstein is the real monster for he stands by while a benevolent creature is abused by society, and he stands by while many innocent people die because of his negligent creation, and the whole time all this happens, he can only think of himself.
How would we measure humanity in either of them? Victor sets out to conquer death, certainly a noble and highly "human" intention. He makes mistakes that isolate him from other humans, mistakes that make a kind of monomaniac of him, but I don't see this as a failure of humanity, but rather of judgment.
The creature is born something of a "noble savage," born innocent, born with no "nurture" to influence, whose "humanity" is destroyed by that fact this his creator doesn't love him, no do the other humans he encounters in his travels. So he forfeits what we might consider his humanity and goes on a killing spree.
So at moments they were both equally human, and they both lost some of their humanity because of internal obsessions or external treatment.
If you're asking me who fell the furthest, I'll have to pass ....
I think that the monster is more human than Victor because of his lack of control about his own predicament. In my mind, Victor's creation of the monster and then the abandonment that follows creates a void within the monster that arouses empathy in the mind of the reader. Certainly, the monster's plotting and exacting revenge against Victor is deplorable. Yet, Victor is more guilty of abandoning him and the sin of deliberate cruelty in such abdication of responsibility. The monster is acting upon the circumstances that are placed over him in such a predicament. In this light, one cannot help but feel more empathy for the monster who has to end up rearing his own sense of self. This is in stark contrast to Victor who labored for two years and then when confronted with the harsh reality took off from the situation.