Oh gosh, I couldn't choose, I love them all. However, I never cared for opals at all until I was at Tiffany's in New York & saw GOOD ones, and was amazed. I guess I had only seen cheapie ones all my life. The ones at Tiffany's look like the pictures that moomies posted, just gorgeous.
I adore sapphires, emeralds, amethysts, rubies... I don't care for garnets. Oh, and I love aquamarines....
A lady I know has a green diamond. It's very striking. It's a deep green like an emerald, but for some reason it doesn't look exactly like an emerald.
Gawd, I was wearing an amethyst ring one day, and this woman (a stranger) asked me if it was a "purple ice." I guess she watched home shopping network way too much.