I know you aren't supposed to but, of my four daughters, the first was my favourite probably because she was born with a slight deformity of her spine that had to be corrected so she spent some time in hospital as a tiny tot. Do you manage to hide it? Hopefully I did.
My daughter with my second wife is my favorite. I think it's because I actually get to help raise her and my wife respects me as a capable father. My ex treated me like a complete idiot all the time when it came to the kids so I never really got to enjoy being their dad.