Take a look here:
http://www.ntpog.org/reviews/filters/filters.shtml
This guy has cut up a number of filters and posted the results. IMO the important thing to note is that the ubiquitous 15400-305-POH made in Canada is the same thing as a Fram filter. I read something from Fram recently defending the use of those cardboard end caps. I also have friends who swear by Fram filters. I've never had one fail, but I'm not too crazy about having cardboard in there as the means of holding the pleats together. Since most of us change our oil pretty frequently, this probably isn't even an issue...just personal preference.
Bogatyr