Comparing fleece to wool is like apples and oranges. I consider the weather when I think of fabrics to wear hunting. Hot to cold, my ranking system would be cotton, fleece, wool. And with so many light and mid weight wool offerings, i pretty much ignore fleece.
There is some high quality fleece that seems like it's pretty good stuff, but no way is it BETTER than wool.
I have worn wool in some very ugly conditions, and it has never let me down. I suppose if I lived and hunted in the South, my opinion would be different, but up here, for me it is wool, wool, wool.