Cerdan was quicker all-around and the better technician, but who can say for sure how he'd handle the big bombs of Ketchel. I think Cerdan might be able to outspeed/out-skill Ketchel to a decision, but I can see Ketchel getting to him in the mid or late rounds and scoring a stoppage.
From what Ive seen of Marcel he is clearly the superior boxer and technician in this matchup. Not sure Stan has the skill level to make his strength and power work for him in this one. Having really seen anything to suggest Marcel has a chin that will be a liability for him..though with Ketchel it often didnt matter anyway.