Upper or lower deck?
By and large, the upper and lower decks are fairly similar but there are a variety of reasons to choose one over the other.
The upper deck in general has better views and is substantially quieter, being further away from the wing and hydraulics of the aircraft. It’s worth noting that the A380 is already one of the quietest aircraft in existence – so quiet that you genuinely cannot tell during take-off when it has left the ground if you are not by a window.
Window seats along the upper deck also benefit from an additional seat-level storage compartment which can be useful for storing things securely that you want to have easy access to.