Try them all! nd dust only one lowest branch. Dust only very young flower. Then you can grow out the seeds to test.
One male plant will generate enough pollen for a dozen gardens within a week or two. I kept my pollen refrigerated. So, it can be used for many future grows.
Warning, there can be more than one set of chromosomes in modern big autoflowering weed. People increase yeild with polyploid. ANd you may get less than 1/2 female. And there may be some hermies mixed in.
I think best way to breed auto is to use pollen from sex reversed females.
Good luck - hope your breeds with be famous.