We can’t say for sure as it depends on what you prioritize and consider to be important. When it comes to sparkle and brilliance, cut is the most important aspect as it has to do with brilliance and the amount of light reflection. If the price is the matter, carat weight affects the price the most. Color and clarity also influence the overall look and value of the diamond. That’s why there isn't a single most important C among the 4C’s, as your priorities will eventually guide your decision.