The only defect I've found that is a show stopper would be one that some one got after with a Brillo Pad. Scratches, some balsam seperation at the edges, even 1/4 inch chips doesn't seem to hinder much.
As to favorites......they are all like a beautiful women. Who wants to choose? Ya gotta love them all. Yesterday I made platinum prints all day from negs made with a $48 lens. But I still think my Struss was worth the 1.5K I paid.