I'm going for MysteriousFellow's. I know it's the underdog, however:
1. It looks like something that is solid enough to damage, but no so that status would effect it.
2. It looks like it could pack a punch, and since when did Guts have anything to do with physical apperances? Guts = Bravery. Swellow is case in point. Does it look strong as Staraptor? No. But it's pokedex entry states that it and Taillow are very brave pokemon.
3. Auto Magic Coat. I can see an idea with MF's design, it could be redicted in the swirling clouds. A Buffalow? No. A Narwhal? No. They don't seem like they'd reflect status, they just seem like they'd run head first into it /burrow under to avoid it.
4. The people saying: 'Ground/Ghost' need to wake up, in my opinion. Sure, it could pass as a Ghost type, but it could also pass as a dark type as much, if not more, than the other two. It looks sinister. It looks threatening, the way it's hunched over. It looks EVIL, like a dust-snake. I mean, as a sprite, how on earth would you tell it's a Ghost-like pokemon, without the slightly fainter part near the hole? If it was roughly the same coulor/shade, it could pass Dark/Ground with no issues whatsoever, and there would be nothing in the design itself that screams 'Ghost' anymore than it screams 'Dark'.
5. In my opinion, it's the best design. Also the most implementable. Imagine getting the detail for the other two into a sprite X_X.
@ Omega: True, we just had a cloud. But since when were other CAPS valid arguments? And, compare the detail in say... Doug's design, to E-Vire, and Doug's has FAR more. Those intractate lines are far harder than the odd stripe. Legends always have great detail, because they are legends (And even then, Doug's is arguably more detailed than those two as well). I must admit, this holds true to Doug's Buffalo than to the other design.