Either the Armor section or the Minipet section (since they are "cute collectibles" too)
And, as mentioned, it'll be a way to show how long we've been around, and we wouldn't like to lose these collectibles once we move to GW2.
The festival hats provide no armor so would be out of place in the Resilience monument. But, as Frozy said, they are a collectable just like minipets and show your "Devotion" to the game.