the 209 is perfect for the fluidline. I wash it each time after I use it and form it back into its perfect little shape to use again. This is, IMO, the most precise little brush.. but practice makes perfect, and a steady hand. It is my go-to brush for everyday, and you can make the best little cat eye with it without going overboard for a day look.
I also love the 266 too
But, if I was forced at gunpoint LOL, 209. All the way.
EDIT to add: And I DON'T have the steadiest hand!!