I can't say much about sexual abuse on children (and anyone for that matter) except that it sickens me.
Physical and mental abuse can shattered a child and it takes years to glue the pieces back together. Throw some bullying in the mix and you have one ****ed up kid. I speak from personal experience. My dad didn't like me too much. He favored my brother. Kids can sense damaged kids.
As for what's worse, I'd definteky have to say sexual abuse. You can recover from physical/mental abuse, but sexual abuse seems, at least to me, like you'll never completely heal. I guess you never completely heal when either's inflicted on you, but sexual abuse seems a lot more severe to me.