Which diamond is most valuable?

Can you please elaborate on the criteria used to determine the value of a diamond? Is it based solely on carat weight, or do factors such as clarity, color, and cut also play a significant role? Furthermore, are there any unique characteristics or rarity that can further elevate the value of a diamond, making it stand out as the most valuable among others? Additionally, are there any specific types of diamonds, such as those with exceptional fluorescence or inclusions that resemble natural patterns, that are highly sought after and considered more valuable in the market?