is this 777 the old UA 3-class, or the CO-style 2-class configuration? (you say 'new BusinessFirst Cabin', but that can mean various things.
Personally I choose 777 over 767, as I enjoy being in the larger plane. But, the seats (provided it's the CO-style BusinessFirst seats) should be the same.
I usually choose one of the middle seats, on either plane (on the 777 both seats in the middle have aisle access), but I find little difference between the two.