The rear section of the upper level is a nice place to sit in the A380 as it’s quieter than downstairs. In addition, the upper deck economy rows are 2-4-2, where the lower deck is 3-4-3, so while they’re almost certainly the same physical seats, the rows feel less crowded.
https://www.reddit.com/r/travel/comments/135mzot/heathrow_to_johannesburg_on_ba_airbus_a380_should/