what vendor for quality parts?

There isn't one vendor who will have all of the best stuff. I like the ones that list different quality reproductions such as N.P.D. If there are several parts of different quality, they list it in their catalogue. Some may prefer the cheaper part for a daily driver while others may be willing to pay alot more for a concours quality part.
 
First off, don't confuse repop manufacturers with OEM or NOS parts. Usually the latter is always prefered but there are exceptions, and there are varied examples of each.

Also don't confuse part makers in general with part vendors in general (there is a very small amount of overlap). If you are asking about vendors you are going to get contradictory results due to the variances in each person's experiences with the many dozens of companies that sell parts for our cars.
 
Most vendors buy from the same few manufacturers, and Scott Drake makes most of the common repop parts, so I've found that there isn't much variation in parts quality except when it comes to sheet metal. However you need to stick with somebody who's advice you can trust. I've used Mustangs Unlimited, CJ Pony, and Mustangs Plus, all with good results. I like the Mustangs Plus catalogue, since it contains some helpful repair articles and tips.