I'm going to restrict this to cards from the 1950s that I actually own. There are only 49 of them and most are Phillies. Looking through them, it was no contest.
1958 Topps #230 Richie Ashburn
I got this card in 2007, paid $7.80 for it on eBay. It's in pretty good shape and is a great looking card from a great looking set.
I grew up listening to baseball on the radio and for most of that time, Richie Ashburn was the Phillies color man. I don't really remember him as a player but I loved him doing Phillies games. He worked as a Phillies broadcaster from 1963 to 1997. He was planning to retire after the 1997 season but he died of a heart attack, at age 70, in his hotel room after broadcasting a Mets-Phillies game on September 9, 1997.
A fact we didn't know until he passed is that Ashburn and my father, who also loved Ashburn, were born in the same day.