I always like shavings with a layer of straw overtop, personally. Nice thick, comfy bed for mama and baby(ies) and the straw stays cleaner/dryer for them with most of the gunk absorbed by the shavings underneath.
Only downside is that it’s harder/takes longer to clean.
I use the fine shavings under and hay on top. Well not the $20 a bale feed hay but, some that maybe got rain before baling, isn't bad if eaten but less nutrition and less costly. Straw just doesn't work well to absorb, lay nice, clean out, etc...mostly. shavings under absorbs the pee better. I have dirt floors.