If you're only going to smoke one or the other occasionally, I say go with the OGS. If you plan to keep one in a regular rotation (especially if its in a dedicated or semi-dedicated pipe), I think the Dunhill really, really, REALLY comes out of its shell once you start to get to know it.
I've never been disappointed by OGS, but then it never really surprises me. Dunhill flake is a bit pedestrian as a once-in-a-while smoke, but when I go back to it over and over, it starts to outshine a good many flakes.