Ortiz by the thinnest of margins is the better fighter. The problem is that Chisora's style gives Ortiz what he wants, the lumbering Ortiz doesn't wanna chase people, and he won't have to, and he definitely has the ability to clip Chisora with something very hard. Chisora while durable, is not Oliver Mccall and can be stopped. That being said Chisora has the better wins.
This fights is in talks according to Hearn. Considering Ortiz went life and death with Martin I reckon Chisora KOs Ortiz early to mid rounds.