insulating a 6-7in flat garage ceiling using r21 mineral wool or r19 fiberglass

I have a 1 car garage. What’s better to install between rafters that are 23-24 inches a part: r21 mineral wool which I will cut to fit since it’s 15in wide or r19 fiberglass which 23in wide. I am trying to maintain temp in the garage the best I can with such a thin ceiling. Anyone have experience with such a thin ceiling?

Last insulation was faced 50% r13 and 50%r19 fiberglass and it was too hot inside so I took all that out, now I see the joists are 24in apart I am kind of limited on options in a way