I like opals, moonstone, and labradorite! I own both besides opal. They're all quite pretty. I always like learning about the history of supposedly "cursed" stones, or their previous uses in paints and medicine.
My favorite gem is chrysoprase. Huge fan of opals and watermelon tourmaline as well. I like the very vibrant ones. My parents got me a gemstone box for christmas as a kid with a polished and unpolished example since I was a huge jewelry channel fan. I don’t have a pic at the moment but it’s pretty cool. Edit: also rainbow bismuth is so pretty!