I think I've tried so many brands of long underwear including Craft, MH, Smartwool, Ibex, EMS, Mammut but never found anything that kept me really dry. I've used underwear mostly use my base layers while backcountry skiing so I'm either pumping out the sweat on a climb or cool on a descent. It's a tall order for any garment.
The Phase AR top is far and away the best I've tried yet. Seems to stay dry in all situations and has surprising warmth for a thin layer. I couldn't be more impressed with the piece and immediately ordered up a second top. Well done Arcteryx!!