A great question! I love all of the Bowman sets from the '50s and a few of the Topps ones. I'll throw in some votes for:
1950 Bowman. Love the color on these cards and the smaller size.
1955 Topps All-American - Iconic tribute set with incredible star power that goes all the way back to the beginning of American Football.
My two favorite odd ball sets from this era, though, were mentioned above.
1950 Bread for Health - the only football bread label set produced.
1959 Bazooka - incredibly hard set of 18 cards that copies the baseball design from the same year
jeff