100% cotton thru and thru, I've had some nightmares with trying to do cotton/poly on a quilt top and as much as I like polyester batting for some things, I'd prefer to use cotton batting for my quilts.
My sewing machine is extremely picky when it comes to thread, it has to be 100% cotton or I have to forget about sewing at all. I was trying to piece a table runner for a friend with polyester thread, no matter how many times I changed the needle, stitch length, tension, my machine would just shred the thread to literally nothing.