To be honest, I think most of those sets are kind of obvious (ZOMG, CScarf would do wonders to help Heatran), but since that's not taken into consideration, I went with MixApe. Being able to bring down the old dreaded SkarmBliss combo is a plus, and he's just overall so useful.
Now if this was for a truly unique set, I'd have chosen ChainChomp. Granted, Draco Meteor on any dragon type is a bit obvious, but ChainChomp shines in being able to also go physcial with SD + STABed EQ as well as having FB for coverage against Steel types.