Shape follows the dessert
Start with the question of whether the dessert needs to be seen. If it has layers, like a tiramisu, a trifle or a cheesecake in a glass, you want a straight wall with no waist, because every curve distorts the lines. If it is one single mass, like mousse, panna cotta or chocolate cream, the shape may well be rounded and a coupe or a low bowl works more pleasantly.
In size, the models here run from 18 to 42 cl. For a portion after a three-course meal, 18 to 22 cl is plenty, because a dessert that is too big gets left standing. For a dessert as the main event, with ice cream, sauce and cream, count on 25 to 30 cl. The larger sorbet coupes of around 40 cl are more presentation pieces. Choose as well between stem and no stem: a footed glass is more festive and keeps your hand off the cold dessert, while a stemless glass stacks better and fits more dishwasher baskets.