Ring Concierge founder Nicole Wegman designs and sells bespoke engagement rings on Instagram and advises clients to allocate budgets toward carat weight, not color or clarity. A round diamond is the best-selling shape for engagement rings, but it is not a best seller at Ring Concierge: The classic look costs 25 more than all other shapes. Wegman said she aims to provide clients with the biggest bang for their buck without sacrificing the look of a ring.