Economy seating on the A380 is 3-4-3 downstairs (A,B,C - D,E,F,G - H,J,K) and 2-4-2 upstairs (A,B - D,E,F,G - J,K) where there is a small section at the rear of the aircraft.
The 435 economy seats have a seat pitch of 32", width of 18" and a 10.6-inch AVOD TV screen.
Upstairs, row 79 and seats 80A,B,J and K look good choices. Row 75 is used for bassinets.
Downstairs, seats A-C and H-K in rows 31, 42, 55 and 66 are also good. Note also seat 60D, which has unlimited legroom due to there being no seat in front of it - the space is left clear as there is an rescue hatch there.