1 v 1
Many v 1
The crew fights coordinated well, but the Yonkou fights will be like CP-9. The crew will be against strong opponents that will prevent teaming up. The Yonkou will be like Lucci at the time, only Luffy stands a chance. Big Mama and Teach he will want to beat because he does not like them. Kaido unless given a reason will be fought against like Shanks. In Luffy's mind the pirate king has to be the strongest. he would have to win in a spar against Shanks to prove he is worthy to be Pirate King. I do not see that battle ever happening against Shanks. There battle would be short maybe a one punch each and Luffy returning the hat.
It will more than likely be 1v1 because Luffy has to be the one to take down the captain of another crew when they are strong. If it takes his crew to defeat a captain, then he can't claim the title of a Yonkou because it took his entire crew. When getting that title, you are saying that it has to be a captain vs. captain in that situation as they are the one that is recognized as the Yonkou. Not their crew, but the captain.
I further think that because it fighting Moria who was known to have once fought equally agianst Kaido (I'm thinking it was before Kaido grew to be a Yonkou), Luffy was the one to take out Moria. So it has to be a captain taking out another captain.