Then when the season's over and you're done wearing it ... you can add it to your "used" collection..
It depends on who you like and what other shirts you have. If you have a DP juve or any other DP Italy, then Get Cannavaro or vice versa. If you don't any other jersey of those two players, ask yourself two questions:
1) Which player do you like more
2) What position do you play in when you play football (or Which player's playing style is more similar to yours?)