On the 763 A-F is the most restrictive since they open to different aisles and have a wall between them. If you want to sit across the aisle from each other you will want to do F-K.

Personally I would choose 1A-2A as it is in a private aisle and conversation capability is about as good as it gets on this plane.

On the 77L there is no wall on the aisle next to A so all seats are across the aisle from each other. The catch here is that they are staggered so you will want to get 1A-2D to be as close to directly across as possible. Last time I was on the 77E we did 6G-6K and it was just okay for conversation due to the stagger and the fact that row 6 is very isolated due to layouts. The best alternative might be to do D-G as there is a retractable partition between them, but you're sitting at a weird angle to each other (think \ / with your heads at the bottom of that layout). I've never sat in this layout so I'm not sure how well it works. If you choose these seats take row 6 as they are slightly more private than the rest of the rows.