I like #11s for shaping pieces and backgrounds. They're large enough for me to go through many times with thread, but small enough to create a recognizable shape. I also use them as decorative beads in some cases, they stand out nicely at the edges of my leaves, or create a subtle change in fringes or the swirly "worms" I like to do for depth. See the Steampunk Choker. I keep #8s around for stuffing shapes. I didn't want this nose to collapse, but there isn't one single bead that would create the nose shape I wanted, so I just made the nose the way I liked then stuffed beads in and tapped them in with the head of a pin or a paperclip.
Here you can see the base beads before I beaded on the second nostril.