Logan is picky, so I tend to use capsules instead of the liquid for him, but I'm considering getting liquid next time. I currently have him on Welactin, and it's free for your SD if you're a member of IAADP (*cough*Em*cough*).
I used to use it on Gavroche, but now that his thyroid levels are fine, he doesn't need it anymore. Gavroche eats anything, though.