Well, this is my first card flip event and at first I was thrown off due to the Knights not giving you hints when you mouse over cards.

After I figured out that the rewards seem to be based on what kind of trim the cards had though (gold trim meant things that are 5* rarity like level 100 manyu, silver trim meant things that were 4* like three of the four pieces of event jewelry, etc) it got easier to avoid Nazuna cakes and pick up the 'good' rewards instead. It doesn't hurt that the first five picks per set of cards are half off in terms of their cost.