The choice is a matter of personal preference. When a diamond is cut to the right proportions, it displays brilliance and fire. When a diamond is well cut, light is reflected from one facet to another and then dispersed through the top of the stone. If it is cut too deep, some light escapes through the opposite side of the pavilion. If cut too shallow, light escapes through the pavilion before it can be reflected.
Diamonds come in different colours.
The 'fancies' - blue, green, pink and yellow etc. are very rare and expensive. Colourless diamonds are most precious, as they allow white light to pass through easily to be dispersed as rainbows of colour. Diamond, being a natural stone, often contains small mineral inclusions. The fewer and smaller the inclusions, the better is the passage of light through it. The weight of diamonds is measured in carats.