Honestly, I think there are a lot of things to like about both poly and cotton.
I've used both. And down here in South Texas, I've found that the cotton batting 'feels' too hot, while the poly batting 'feels' like it is lighter and not so warm. Since we certainly don't need a lot of quilts to capture the warmth like we would in a more northern climate, I tend to use poly more frequently. I've never had trouble with it bearding, and I done both hand and machine quilting. Maybe that depends on what brand you use?