I think Holmes easily beats Johnson, outboxes Louis, and does the same to Frazier, possibly stopping him late. I think he beat Maricnao in a much tougher fight than most see, and takes out Foreman later once he slows down. Dempsey really was a front runner type and too easy to hit. Holmes via UD. Lewis and Ali are his toughest match ups, so I'll pick the losses here even though the fights could go either way.
To best Prime Holmes you would need to outspeed him or be technically competent enough to counter his jab, which he constantly dropped, with a KO right hand and then be able to follow up for the win. That being said who could beat Holmes: Ali - Prime Ali outspeeds Larry hitting him at angles all night for a Unanimous 15 round win orlate fight tko. Louis - Louis had a trip hammer right hand and an unmatched offense. At some point Louis catches Holmes with that right over that low left jab and the bout is then soon over. Marciano - Again a fighter with a killer right hand. It finds its mark at some point to end the bout. Tyson - Certainly Holmes was the greater fighter but here again Tyson had the skill to counter that jab. Mid fight tko. Dempsey - Similar to Marciano and Tyson, Dempsey had great power on both side left and right. He also had the technical capability to counter that Holmes jab. Mid fight KO.
Holmes is my 5th favorite fighter of all time. That being said. I feel he loses to everyone on this list except Marciano, Lewis, Johnson, and possibly Foreman
Holmes is even money or better against everyone out there. His toughest bouts would be against Mike Tyson, Louis, Dempsey, Ali, Liston, Frazier, Bowe and Lewis.
He could well lose all of those, but.... IMO, he's a slight favourite over Dempsey. Marciano is a 50-50 And he loses all the rest.