I'd go with Impish, actually. The only common Special attack he's weak to is water (Surf and the likes), while he's 4x weak to both Ground and Fighting. And in the competitive world, a 4x weakness to Earthquake REALLY hurts. But he has the Defenses to take an Earthquake or two if more attention is spent towards his Defense.
Or you could go the old fashioned way: Impish nature, max EVs in Special Defense and HP (standard Scizor-like set). And then just watch out for Grounds and Fighting.