I personally like how derpy the chickens look, but my favorite chicken has to be the void chicken, i buy the void egg as fast as possible once I unlock the sewers.
I like the Dinosaurs best as they're Dinosaurs! Like real (pixel game) Dinosaurs on your own farm which you can name after your favorite kaiju. Also they only lay eggs once a week and with the v1.6 Books and Crackers you can sell those directly for decent g so they are the very definition of little effort. Which is the way to my heart.
I'm a bit of a fan of golden chickens as some may know.....
I do really love the look of ostriches, just wish they weren't such a pain to get in large amounts, I'd love a large ostrich farm but never feel like bothering with it.