If she asks you, your partner is always the most beautiful at the party. It doesn't matter if it was a Supermodel convention or the Sports Illustrated Swimsuit Model party. If she says "What did you think of ____" or "I think ____ is prettier" you just say "___ IS pretty but she doesn't have your ____" (insert her best trait here.) She is asking you to affirm your commitment to her, not to hear how attractive you found other women at the party.