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; if it's cold enough a layer of wool and a layer of poly fleece. There may be an outer layer depending on condition and circumstances. That outer layer can be nylon or wool -- depending. It's very situation driven. Pants will be merino wool long u/w under nylon or fleece pants. Socks is wool and wool, liners and socks under boots.