I've posted this before but I have used JC Penny's Towncraft brand (both blend and 100% cotton) and Lands' End's tees and they were both perfect. I would usually turn my nose up at any clothing by them but these tees were great. They lasted forever (only got rid of them because they started to yellow) and no warping / mutating in the neck and sleeves at all. I think the Towncraft blend were slightly form fitting (which I like) and the Lands End were a little baggier (not too loose though).
I tried 2xist and the fabric and stitching was nice but they are short, small, and tight fitting in the arms (and I'm not THAT big - 5'11 / 185 lbs.) Plus, after the first wash, they (for lack of a better word) mutated around the collar. I bought them from STP on sale but I won't recommend them unless you are a smaller, thinner build.