I bought several ase layers prior to my elk hunt this year,some sitka poly pro tops, and some merino wool tops and botttoms. When its hot, I liked the poly, but for the most part, I prefer the merino. AS mentioned, it has a great natural ability to not get stinky. That poly stuff gets ripe fast. I had a few prs of poly boxer briefs, and 1 pr of merino briefs. The poly would get funky in just a day, where the merino didnt stink even after a couple days bivy.
The price difference between UA, or sitka poly layers isnt much different than the merino,and well worth it. I definitely plan to pick up some more merino layers. Love the stuff.