I recently bought a 20 gallon Blichmann and I'm happy with it. I doubt you're going to find anyone with one of each to really give you an honest comparison.
I considered a Stout Tank as they had some features I liked but I had seen the Blichmann in person and couldn't really get a feel for the Stout Tank quality online (although many seem happy with them). My Blichmann also came with free shipping via Austin Homebrew and Stout is on the opposite side of the country from me.
Both companies need some serious website work. When spending $500+ on a metal pot, some decent pictures would be helpful; especially of the various features (sight glass, thermowell, ball valve).