With omniscience and omnipotency, you get a God that can create anything he wants, well-aware of whatever consequence that would follow anything he does. He would know that allowing Timmy the Murdering Rapist to be born would result in rapes and murders. Yet he made Timmy the Murdering Rapist and countless others of his kind.
The only way for Timmy the Murdering Rapist and his kin to exist is for God not to be omniscient or omnipotent, or for him to be evil and/or negligent. Therefore we can not both say that he is omnipotent and omniscient and think that he's a good guy worthy of our worship.
For a tl;dr version see
