I am making a table topper & I don't want it to be thick--I am thinking of using flannel or muslen for the batting--what are your thoughts on this?

You could use flannel, but I like the warm and natural batting for tabletoppers because it has more weight to it. It lies flatter on the table.

I've used flannel before but muslin is just another cotton and won't give you any body. Check out the warm and white - it seems a little thinner than the warm and natural.

I would use the flannel over the muslin, both will lay flat, but the flannel would look nicer after quilting IMHO

I would use the flannel over the muslin