© Carnage.
While Venom is the parent of Carnage, which would suggest that Venom should be stronger (since it was a simple asexual reproduction), Carnage has considerably more power due to the fact he was able to bond completely with Kasidy, while Venom's 4 hosts have all partially rejected the symbiote.
There's always a chance for Venom to win, because Carnage is so insane he frequently makes mistakes, but typically even Spiderman doesn't have enough power alone to take advantage of these. In most cases, it takes Spidey and Venom working together to stop Carnage.