Depends on what I'm doing.
If I'm doing sports, fast-and-sweaty, I go for synthetics. In that category HellyHansen, Patagonia, Lowe and MacPac have served me very well over the years.
If I'm out doing bushcrafty stuff, hunting or the likes, I tend to go for wooly base layers. There Woolpower, Icebreaker and Smartwool have kept me toasty warm.
And for longer days hiking or cross-country skating (yes, skating), I tend to use a mix of synthetics and wool, with the synthetics closest to the body.
/ Karl