Most Important Baseball Card!

[bbcard1]

Let me make a pitch for this guy...the 1939 Playballs was the first substantial baseball offering made by Warren Bowman and the Williams rookie was the most significant card in that set. After the war, he rebranded his Gum, Inc to become Bowman and demonstrated that baseball cards were viable product. There is still a small part of the company's DNA in modern Topps and Bowman offerings. I get that this is a somewhat contrarian view, but seemed worth pondering.

[CW]

Thinking a bit outside the box here, but...

the most important card is the one that got you interested in collecting cards.

[JollyElm]

If you had to rank your cards in an orderly stack of "Easiest to sell or trade" to
"Wouldn't sell or trade it even if a loved one's life was hanging in the balance,"
then that card at the bottom is the most important card.

[vintagerookies51]

Important for American history? I'd vote the Bond Bread Jackie portrait. Outside of that I'd be torn between T206 Wags and 52T Mantle. One is extremely rare and expensive and makes the news every time one gets sold, while one is the realistic grail card for many collectors.