"Obama would be easier to beat than Hillary"
Not necessarily. I've seen data that suggests that, surprisingly, women would be more apt to vote for a black man than a woman. Weird, but it makes sense somehow,
You are thinking generically. If I had my choice, I would rather face Obama than Hillary. He has many more weaknesses. And he has yet to undergo the kind of scrutiny that a Presidential campaign would subject him to. He is a dead man walking.