Personally, I love Merino. Lightweight for baselayers, midweight for 2nd layer if needed. Synthetic gets stinky fast when worn several days in a row (for me, at least). I can (and do) wear the same Merino for a full week and not notice any significant body odors. And, if you're not in a hurry it's not too difficult to find some good sales, even at REI. Try to hit their Scratch and Dent sales and you might find some.
