On the 777 the two aisle seats in the centre block have only one seat between them, so on a flight where your row is full the person next to you has an expected 50% chance of disturbing you.

On the 747 the person next to you is guaranteed to disturb you.

Also, on the 777 if the seat factor is 66.7% or less you are guaranteed an empty seat next to you.

On the 747 you have to have a seat factor of 60% or less, which is less likely.

For these reasons I would choose the 777 over the 747, all else equal.