Short answer
Choose cushion if you like rounded corners and want to select the facet pattern and outline by eye.
The look
The softened square can feel vintage, contemporary or both, depending on the facets and setting. Two cushions with similar grades can have noticeably different character.
Use the measurements
Use length and width to separate square from elongated cushions. Compare face-up dimensions because some cushions carry more weight in their depth and can look compact for their carat weight.
What to inspect on the exact diamond
- Decide whether you prefer broad, distinct flashes or a finer crushed-ice appearance.
- Check that opposite sides and corners feel balanced.
- Compare the actual face-up length and width, not just carat.
- Watch several real examples in ordinary lighting before deciding which cushion style you prefer.
Plan the setting at the same time
Rounded corners are less exposed than sharp princess-cut points, but very thin girdle areas can still be vulnerable. Prongs, a bezel or a halo should follow the actual outline rather than forcing it to look square.
If this shape is not quite right
Choose princess for sharper geometry, radiant for a clipped-corner rectangular shape with a busier pattern, or round for a more standardised cut assessment.
Source and limits
Read the GIA cushion-cut guidance. Ratios and grades help you compare; they do not replace looking at the exact diamond or getting independent professional advice where needed.