Well, that would probably be a dual on-card auto of Matty and Clayton Kershaw, although that would more aptly be described as the crown jewel of my entire collection. The below, when considering its rarity; gorgeous design; on-card signature; and difficulty in simply finding, may well be the jewel of my Bison PC.
Numbered 849/880, this ultra-rare gem and exceptionally tough find is Kemp's 2006 eTopps RC. Although there are 880 of them, only 100 were signed and all had to be acquired through the eTopps program. I've seen this occasionally appear on eBay in the eTopps case but never for a reasonable price. I landed this beaut for less than $30 shipped and couldn't be happier with my purchase.