I don't see why so many people are voting Garchomp. Yes, it's dangerous, but unlike something like Salamence, it has counters. HP Ice Tangrowth can come into the Choice Bander or Swords Dance fairly well, and the same can be said for Ice Fang Gliscor/Hippowdon. Suicune and Slowbro with Ice Beam even has a shot at surviving a Swords Dance'd Outrage, making them reliable counters, especially Slowbro with Slack Off. Then there's Cresselia, who can come into *any* Garchomp easily. Ice Fang bulky Gyarados and Ice Beam Starmie are both excellent counters to the Swords Dance set as well.
Physical Salamence has to deal with all of these too, but unlike Garchomp, they have to fear eating a Choice Specs'd Draco Meteor when switching in, and Blissey has to fear a Choice Banded Dragon Claw or Brick Break. Cresselia can come in on either of these, but really cannot stand more than a few Draco Meteors and doesn't enjoy Choice Band Crunches. Then there's the mixed set that has seemingly no counters at all.