I'm thinking DD. He needs the speed IMO. DD does wonders for Gyarados, and I think Haxorus is just a "bad dragon" right now. In a years time I expect he'll be dominating UU or useless in OU; and whether DD or SD is used depends on how many pokemon are faster than him in UU - and I believe it's going to be a lot.
That said, it all depends on what you're using him for. For example, I don't think much of any power up move is good in triple battles (except quiver dance of win), while "dodge" moves like dig, bounce, and fly have been pretty useful in the few I've played.