As advised above, there have been plenty of threads on this.

However, to save you from the dodgy search function, the widest-held opinion is that the 747 cabin is the best as it has no walk-through traffic, is quieter, often has fewer seats, feels more intimate and exclusive and generally has a nicer atmosphere. With the 747, you are also guaranteed AVOD and a larger screen - on the 777, you are not.