767 for me IMO - what can I say, I like a more spacious plane
It depends upon whether it is a PMUA or PMCO. PMUA are narrower and very uncomfortable, nothing more than economy seat that lies flat. PMUA 767 seats are 2-2-2 in BF whereas PMCO are 2-1-2. PMUA in 777 are 2-4-2 whereas PMCO are 2-2-2, obviously more space.
OP, whatever you do, don't listen to this post for advice about the seating, if you want accuracy