The round brilliant diamond cut is known to have the most brilliance compared to other diamond shapes. This cut consists of 58 facets including the table, crown, girdle, and pavilion. The diamond is carefully cut and polished to maximize the reflection and dispersion of light, resulting in a high level of brilliance and sparkles.

The round brilliant cut was specifically designed to maximize the shine and sparkle of the diamond.  The even distribution of facets allows for light to enter through the top of the diamond, undergo total internal reflection, then exit through the top again, producing a blaze of light known as "fire". This is what makes round brilliant cut diamonds so fascinating and valuable.

Other diamond shapes such as the emerald cut, pear cut, and cushion cut have fewer facets, which can cause less reflection and dispersion of light.  The round brilliant cut is so popular that it accounts for around 75% of diamond sales today.

Overall, the round brilliant cut produces the most brilliance in a diamond because of its precise symmetry and maximum facets for reflecting and dispersing light.