I favor Brioni, though this is partially a fit issue as I am fairly tall and fairly thick of neck, so their long and thick ties result in a very nice knot for me, where some ties are just a bit too thin to tie well to my length.
I can't stand Nordstrom suit salespeople generally. It's absolutely impossible to browse there. They won't accept looking around. Before I knew anything much about suits I had them foist off some true crap on me. Now that I do, the few times I've seriously shopped there, I've explained what I'm looking for, and they continue to bring me crap I wouldn't consider buying, and they obviously don't understand why it's crap.
I really like what I believe is called a self-collar. That is, a collar in the style of a dress shirt with quarter inch top-stitching. It should have a fair amount of structure to it. I've wondered recently whether you could incorporate small stays in the collar to give it a bit more body, though I've never seen a shirt like that.
The other important factor to me is length. Fit it a given, of course, but it seems like a lot of shirts that well otherwise are cut too...