A lot depends on the specific charity.
Charities that give quilts to children in the hospital typically request cotton batting (or 80/20) because it holds up to the harsh hot water washing and drying of the hospital laundry, especially since the quilts of some children need to be washed every single day.
Charities that send quilts overseas often request polyester batting because it dries much faster than cotton or wool -- helpful for countries where families and hospitals do not have dryers.