By our scores for diamond, the round brilliant sparkles the most overall. It returns the most white light of the ten classic shapes: brilliance 93 out of 100. The oval scores highest for fire (92) and for scintillation (87). Brilliance, fire and scintillation added together, the round brilliant scores highest.
| Shape | Brilliance | Fire | Scintillation |
|---|---|---|---|
| Round brilliant | 93 | 78 | 80 |
| Cushion | 80 | 73 | 85 |
| Trilliant | 78 | 83 | 79 |
| Asscher | 69 | 80 | 72 |
| Marquise | 64 | 89 | 86 |
| Princess | 57 | 83 | 78 |
| Emerald cut | 55 | 87 | 72 |
| Pear | 53 | 84 | 76 |
| Oval | 47 | 92 | 87 |
| Radiant | 32 | 77 | 74 |
Why
In this answer, sparkle means brilliance, fire and scintillation together. Brilliance is the white light a stone returns. Fire is the flashes of color. Scintillation is the pattern of light and dark flashes as the stone, the light or the viewer moves.
A round brilliant is cut to return the most light to the eye. In our traces, more of the light from long shapes leaves as fire. But they lose more light through the back.
Compare any two cuts in the Cut Performance Wheel, or turn them in light in the 3D Gemstone Simulator.