The Cushion shape is the antique-look cousin of the round brilliant. Comes in many dimensions with only few júst right, be it oblong or squarish. In other words, Length/Width Ratio: Whatever you like! Most of them though carry too much weight in their belly, making them appear smaller than what what its their carat weight says.
Red flag: Choose well between an oblong or more squarish shape and also, make sure you are informed about the difference between the very sparkly ‘Crushed ice’ shape and the antique but more authentic chunkier look.