Cut matters more than size. Here is a straightforward guide to which shape does what.
Follows the body throughout. Needs a fabric with recovery, and a lining — without both it will show every seam underneath.
Fitted to the waist then released. Forgiving through the hip and easy to move in, which matters more at a party than it sounds.
A gentle widening from the bust down. The most universally wearable of the four.
Straight from shoulder to hem. Cleanest on a longer frame, and best in a fabric heavy enough to hang rather than cling.