When it comes to a directory, discussions of Pagerank tend to 1) only relate to homepage PR, not internal page PR; and, 2) the "issue" of PR or Alexa or "strength" tends to be an issue of concern mostly for those attempting to market their directory.
For my money, 99.9% of the PR/AR or strength discussion is hen-clucking.
More important factors:
The editorial quality, and therefore utility, of the websites listed.
The quality of the listings themselves, i.e., is the information in some way more useful than the what's found in the raw SERPs.
Niche or limited vertical focus directories beats general directories.
The directory sends filtered, pre-qualified traffic.
Free listings beats paid listings, but free only goes so far in supporting quality, which leads to a consideration of . .
Volume and placement of ads competing for attention of directory visitors.
The depth of the directory's listings.
The overall professionalism of the directory "as a website".
Thanks for the reply. I agree and it is my long held position that as Google etc. search criteria improves that quite simply content - and top content - is king and that however many billions of pages the spiders crawl that Google's stated goal of connecting search results with relevancy (as it improves) will always lead back to this. I simply meant though which of the two is a more useful generic/catch-all method for loose value assigning - at a glance..?
I usually try to find high traffic directories in my niche based on Alexa. Then do a google search for some of the text on the page where I'll be listed. If the page shows up in the results there is a better chance the directory is getting traffic from the search engines (and not just webmasters submitting their sites). If you get listed there you'll see a bit of traffic to your site and I've found these links help quite a bit in the SERPs.