Suggested by Sonic Cosmoman and Colonel are both powerful fighters. In the manga they even got to briefly go up against each other before it was interrupted. Cosmoman certainly has the edge in long range while Colonel would crush him in close quarters. That’s why I would go with Colonel because he has the speed to force a close range battle. Cosmoman can hold out for a while but ultimately he would be overwhelmed. Colonel was able to trade blades against Bass for a brief amount of time after all. Colonel wins.
Update 4/1/2023 It was pointed out that Cosmoman’s got his fusion with Nebula Grey at the ready so in the end that will be enough to turn the tides here. Cosmoman wins.