Ortiz. Much more proven and accomplished at the weight, and with all the tools, brains, and versatility needed to figure Pac out.
I don't think Ortiz being proven more at the weight has much to do with it all. It's not like Pacquiao isn't proven in his career, and they're essentially the same size. But I agree, Ortiz is the favourite. He'd grind Pacquiao down to the body, and I think he was heavy-handed enough a counter-puncher to to make Pac a bit honest.
I'd probably give the edge to Pac. Ortiz was occasionally troubled by speedsters, and Pac would be a speedster with exceptional power.