It was a tough pick, but I had to go for Owl Eyes. It's just so useful. It's a decent weapon, but it cuts down armies. Especially once you get multiple of these flying, most cards die the turn you get control of the field.
Firefly Queen is fun, and Unstable is a great card, but i have to give it to Owl Eyes. Useful in so many decks since day one, and always will be.