Welcome to FlyerTalk

The best seat in y is a very subjective thing.

Do you want to be among the first Y pax off? - Get one near the front.
Do you want to ensure you get first choice of meal ? Get one near the front or the back of the cabin.
Do you want to maximise your chances of being able to spread out over two or more seats if it is a light load? Check Experflyer for the load, and if it is showing straight nines close to departure, book one in the centre of the plane towards the back.
Do you want an undisturbed night? Avoid seats near the toilets.

When I travel in Y, I always try and book an exit row, especially on a night flight. The seats are narrower due to the tray table being in the armrest but the extra leg room makes up for this IMHO.

Have a good flight

Nick