I chose the DF because I felt it was the most unique offering to date. My mindset was "If Scrapyard had only produced one blade, which blade would have best exemplified Scrapyard as the brand of a leading knife company".
The SS4 is neat but a number of 4" EDC knives have already been done in INFI.
I also agree that the Scrapper 6 is the best all arounder. I love the blade shape, thickness, balance, and Res-C handles. Yet there are other good knives with similar blade shapes and variations of rubber handles.
For me that leaves the Dogfather as the defining blade. The perfect big knife steel (SR-77), combined with a great blade shape, the perfect chopper handle, all at an incredible price point when combined says to me "the DF is the one".