CX HKG-FCO is generally operated by a 2-class A340-300 aircraft. This is called type 34D on SeatGuru's site.
The seating is standard economy seats that you would find on most CX long-haul flights, with personal seatback video screens and AVOD. The seating is 2 x 4 x 2, so personal preference comes into play depending on aisle or window desire, and if travelling alone or with one or more others.
It does not make a lot of difference. I would be going for most forward D or G aisle seat I could score.
As this is a late night departure (just after midnight), assume you are going to want to sleep more than watch movies. In my experience with CX long-haul in Y, there is often a constant demand for hot noodles throughout the flight, so avoiding the galley areas may be desirable if you want to sleep and not be awoken by the constant aroma of noodles being carried past your seat.