Row 3 on the A380 is perhaps preferred because it has three windows instead of two. Being in the middle of the cabin also means it’s not too close to the galley at the back, but you still get the crew passing from time to time in case you need anything.
Left or right hand... well perhaps more important is the side you sleep in, if you are a side sleeper. While the a380 suites are enclosed, the 777 are not. Some people don’t want to sleep facing directly on to the aisle.
For seating on the 777. Single row you would sit in 1A as a solo, as far away from the galley at the front left as possible. This minimises noise and light and increased traffic to and from the galley.
If it’s two rows, row 2 is preferred by some because it is set back a bit more from the bulkhead. Staring at a wall three feet away doesn’t suit everyone. And there’s more traffic than row 2. So on a one row 777 i’d take 1A, on a two row, 2A.
For the a380, row 3, either A or D. (and for couple 3CD)