I'd have to say Wynaut is what seals the deal for me, able to take out any one pokemon (except some houndour), turn any pokemon into setup bait, and even take down something slow with Destiny Bond. It also makes a joke of scarfed pokemon, setup pokemon, and most support pokemon with just Counter/Mirror Coat, or Encore.
Otherwise, I like Gligar, having the ability to go 19 speed on a defensive pokemon is a godsend, and stealth rock, u-turn, roost, and taunt just make it a fabulous pokemon to use defensivley. The only thing gligar has to watch for are water/ice moves which are easily enough taken care of. Immunity to both ground and electric, and excelent defenses means it can come in on a majority of scarfed pokemon and set up Stealth Rock effortlessly, allowing you to break sashes and put pokemon into OHKO range without having to attack them.