The A350 is a newer aircraft, and generally has better tech.

Aside from seating (which we're determined the A350 is a step backwards), the aircraft is smaller (holds less pax), but is said to be quieter. In my personal experience this is a moot point, and is not really much better. You'll be forward of the engines so it will be quiet regardless of the aircraft used. The A380 has the quietest cabin across the whole aircraft, full stop.

The in flight entertainment might be slightly better in the A350.