Re: John L Sullivan vs. Randy Couture, special fight*
Couture. Sullivan was quite good, but his skillset doesn't transition well to a ground-and-pound environment. He took on the American Greco-Roman champion in an MMA at one time and was slammed onto the mat.
On the other hand, the version who fought Kilrain (Sullivan was trained with that same Greco-Roman champion for the fight) may do a lot better. In that case, I'd pick Sullivan.
After the fight, Couture decides to train with "Team Sullivan" to add yet another layer to his boxing.