How The Shape of a Diamond Affects Your Engagement Ring Choice Choosing a ring based on the 4 C’s and its shape can help find the ring that guarantees your partner will say yes! Some of the most popular diamond shapes include: Round Cut: The most popular diamond shape for engagement rings, the round cut has classic and timeless appeal, cherished by so many. Article continues below advertisementHow to Choose The Best Diamond Shape for an Engagement RingUltimately, personal preference is the deciding factor when choosing a lab diamond shape. Article continues below advertisementSource: Unsplash+Lab Diamond Shape FAQWhich shape is most popular? Does a lab diamond shape affect the cost of an engagement ring?