I found Cat's Cradle and Slapstick were my least favourites.

I voted Bluebird here because I love the ending. I'd have that, Galapagos, Hocus Pocus, Jailbird and maybe even Timequake in my top five. They are all worth a read. He may have been a poor husband/father/person during his life but how he wrote was beautiful.

My favorite is probably his collection of short stories, Welcome to the Monkey House.