Between '53 and '56, I would go with '56.
The '53s look better in my opinion, but the player selection in the '56 set is what wins me over. Having Paige in the '53 set is a strong argument for it, but the '56 set has Aaron, Clemente, Koufax, Snider, Banks, Kaline and probably others.
Perhaps I should also admit that '56 Mantle is in my top 10 favourite cards of any era
Good luck whatever you choose.
Cheers,
Richard.