Doesn't there need to be an accounting of the evolution of those events? The more evolved, and perhaps less corporate-dependent a tournament gets, the more likely it is to be held on a classic-quality golf course.
Younger and smaller national opens (sounds oxymoronic, doncha know?) need the largesse of corporations that take their events to corporate-friendly locales.
I would suggest that the most stunning turnabout was the decision by the RCGA to move away from its 23-year prison cell home base of Glen Abbey and take its show on the road. It reaches across from Montreal to Vancouver. Now we have Hamilton (Ancaster), St. George's, Shaughnessy, Royal Montreal and hopefully others in the rotation. If it ever decides to go to Nova Scotia, it will be akin to the Scottish Open going to Dornoch, or the Oz Open playing itself in Tasmania.
My ranking:
US Open and British Open (not a national open but no other category will have it)
Canadian Open and Aussie Open (good clubs balanced with clunkers)
Scottish and Irish (at least they move around a bit)
Japanese (potential to hit Colt every now and then)
The lurker will be the China Open, if it ever gets to some of those new builds by guys we love.