Ask the staff which cat they think is a great cat, but has little to no chance of being adopted. They'll probably know who deserves to go home with you. Until recently (I started working more) I was volunteering at a humane society. I'd always have been able to tell you who I thought deserved it most. (my shelter was no kill - I don't think I'd have been able to bear it otherwise, but kitties could stay a loooooooong time before finding a home or passing away naturally)