Well as long as we can make it up as we go, and excluding cards and card-like items:
Favorite BB item: 1955 Koufax photo after his 1st big K game:
Favorite FB item: 1966 Chicago Bears Dick Butkus team issue:
Favorite boxing item: 1915 Benny Leonard by Hall Studio:
Favorite basketball item: 1960s Dolph Schayes signed premium:
Favorite hockey item: 1964 Terry Sawchuk photo:
