Wool is the favorite of many quilt contest entrants, for it's softness and dimension. Wool shows off the quilting very well.
Cotton provides that antique (crinkled) quilt look, after washing.
Polyester gives you that puffy, comfy and snuggly look, even after washing.
Some quilt contest entrants use a combination of wool/cotton or wool/polyester to combine the look/feel of both.
So, it all depends on the look you are going for.