In no particular order of preference, I like rubies, sapphires and amethysts. These three, in their deepest but still transparent shades of red, blue and purple are a sight to behold and probably quite nice to own too. Diamonds are, obviously, expensive but being frequently colourless (not always), I find them less pleasing to the eye. Emeralds I can take or leave, depending on whether or not I like the shade of green.