I wouldn't pay the extra for a Qu T. I don't think the slightly improved fineness of the fiber (17.5 micron vs. 18.5) is worth the extra price (although I haven't tested it to find out).
If you don't need 17.5 micron stuff, the Woolies shirts to be worth it, and the same with the Echo T (it's in the outlet).
As for Ibex vs. Icebreaker, I find both to be high quality and non-scratchy. However, the fit is the big difference. Icebreakers tend to run a big bigger, and as a result they are a little looser on me. Ibex stuff feels more like a second skin.
I initially preferred Icebreaker's boxers, but after dealing with wear and tear for a year, the Ibex stuff has held up, while the Icebreaker stuff has deteriorated a bit (still quite wearable though).
The one Smartwool shirt I have is OK, but doesn't compare to Ibex or Icebreaker.