I've got one of the original Backcountry.com merino T-shirts, and it is awesome -- as good as anything I've seen from Icebreaker. Thin and wonderful, stink-free, and looks nice enough for daily wear.
The Stoic ones I've tried on -- a roommate had a few -- and they aren't as form fitting. Baggier, and I didn't like the cut as well. They don't look as good on and the colors aren't as good, either.
Still a decent value, but I wouldn't rush out to get them unless they were an amazing deal.
What I have been impressed by are the Stoic and Backcountry.com jackets. I've got a Shift jacket, and I've purchased a hard shell and a wool jacket as gifts and for the money when you get them on a good sale or SAC, they are the best value jacket's I know of anywhere.