I've never seen any marks on the very top of a completely round ball, so I'm assuming that the top of the ball doesn't make much contact on most couplers. I didn't find any references to a difference when I searched online for it either. I would have to say, in all likelihood, there's no difference at all.
2015 Chevy Silverado LTZ - HD tow package
2017 Rockwood 2703WS Emerald Edition