I think it really depends on your deployment. A few examples:
Each of these benefits differently from different approaches.
In the case I mentioned involves mostly items 3 and 4, so it had to be both keyword-targeted and brandable. I consider that a tougher case than an optimized traffic site (multiple keywords good) or a brand site (uniqueness is good).
As for aftermarket domain resellers, I always review those as well and consider it in the mix, but that's not easy either. At $500 a pop plus the work involved typ. it ain't cheap either. My whois tools allow browsing of registered and deleted domains, so that is part of my review. I only need to go to a vendor if I want to inquire as to availability of registered domains, and that's usually after I have looked at the active site.