Gems : Sapphire

Sapphire is the usual name for transparent corundum. Sapphires are usually blue, but they can be almost any colour.
Very dark sapphires appear black, and aren’t very attractive or desirable. Equally, an extremely pale sapphire would be colourless, and although rarer than black sapphire, is not particularly attractive or valuable. The most desirable sapphires are generally those with an intense blue colour, and plenty of sparkle and life.
Ultimately, which is "best" is subjective, and our usual advice is to buy whichever colour of sapphire you personally find the most attractive.