A black cocktail dress is the least risky thing in a wardrobe and, handled badly, the least interesting. The difference is construction. These are our black cocktail styles chosen for what they do rather than what they avoid — bandage knits that hold their shape from the first drink to the last, ruched bodices that move with you, embellished and crystal detail for evenings that call for it, and strapless, sleeveless and long-sleeve shapes across mini and midi lengths. Bandage is worth singling out: the fabric is dense enough to smooth rather than cling, which is why it lasts a long evening better than a light jersey. Keep the accessories to one point of interest and let the cut carry the rest.