I'm old school, and love flatheads. I was raised on Briggs & Tecumseh's, and I'm very partial to HS40's & HS50's. I also agree with what was said above, flatheads for vintage bikes, and clones for newer/modern stuff.. There is just something that makes me cringe when I see a great old vintage mini with a clone on it that looks completely out of place for the frame.. Just my 2 cents..
-Marc