I'd say this. How a person responds to adversity defines him more than almost anything else. The boxing ring is a truth chamber (to borrow from Teddy Atlas).
Cotto's best win is Mosley. That was a close fight that coulda been a draw or a 115-113 win for either guy. But it was a good fight against a great fighter who was older but still game, and Cotto showed he was on the level at that time.