Ditto -- It's not an either/or question, both have their strong points.  I like pure Merino wool next to skin.  Layered above that will be either another layer of wool or poly fleece;........
Big Ditto on that statement!   It's all about proper Layers, and a base layer of Merino wool is a great Start, then a fleece, then a shell (dictated by the conditions)..   I have yet to burst into flames next to a fire, and have been around PLEANTY.