Hmm... tough to choose 3...
#1 1947 Bond Bread Jackie Robinson (Batting - White Sleeves) - For the simple fact that it is very tough to find any of the 1947 Bond Bread cards... this is probably #1, but will be replaced if I can get my hands on the card of him leaping for the ball in front of the scoreboard...
#2 1949 Leaf Jackie Robinson - I mainly collect Jackie Robinson cards... you can't go wrong with this one.
#3 1948 Bowman Stan Musial - I was going to pick my 1955 Sandy Koufax, and probably would interchange the two on another day... but today Musial is #3.
On a side note, I also love the '61 Juan Marichal simply due to the Dominican historical element of his birth city being known as La Ciudad de Trujillo when Trujillo was in power... Being married to a Dominican, and having a son that is obviously half-Dominican, it makes for a good conversational piece.