I think Shank will take it because he's a bad matchup.
Kaido may be stronger than him, I see Shank as deadlier.
Kaido love take hits, break the mind of his opponent and have a good fight.
Shank don't seem to bother of those, a supernova come to argue with him... He cut his arm... No waste of time.
Against Luffy he may not be as cold, but in a real battle condition he will go for the win as quick as possible... While Luffy is like Kaido, more playing around and no go serious at the begining of a fight.