Since I started using only natural stones (i.e. Amethyst, Aquamarine, Jade, etc.) I have found that I like some stones more than others. Maybe it's their color, maybe it's their versatility or maybe it's the energy they give off. I also prefer certain shapes/cuts of stones, and it changes from time to time what I like.
These days I like 4 & 6 mm rondels and round. They flow really well within a design. As for stones, well, I have many favorites. I tend to like blue stones like Kyanite (blue with striations of other shades of blue throughout) and Aquamarine. I especially like raw Aquamarine. I don't like it to consistent in color. Yellow is my favorite color in the world, but for stones I have rarely found a shade of yellow that tickles my fancy. I love green, but not all greens. There is a green Kyanite that I find to be really rich. I do like Jade and it comes in sooooo many different shades these days (a lot of which are probably dyed, but I don't really mind). Despite being a family of means, I was inducted into the pearl sisterhood at a young age. My mother is a big fan and made sure that I had my own pearl earrings at the age of 11. I felt so elegant, I had no idea that because they were freshwater and she'd gotten them at a jewelry show (my father was in the biz many years ago) that they probably cost her about $10. So I find whenever I make something with pearls in it, I think of mom. Or I give it mom.
Other favorites I have, in no particular order: Jasper (so earthy, and so many variations of color), Blue Lace Agate, Sunstone, Rhodochrosite (I'm not much for pink, except this one) and Gaspeite (although it's impossible to get anymore). All that being said, when a stone moves me to create, it doesn't matter if it's one of my favorites or not, it is at that moment. And really that's all that matters.