At 6'2" I think the 777 seat may be better because of foot room particularly if you have a large foot size. Depending on your size(width) you may find the 767 more accommodating because of the increase width of the seats. With my dimensions 5'8" and 200+ pounds I prefer the 767 seat and really enjoy the middle seat.

In any case if sleep is a priority and 767 middle seats are unavailable, I would opt for a window seat on either aircraft so you are not disturbed while sleeping. While some people find the footwell size on the 767 to be a problem at 5'8" and a 8 1/2 shoe size it has never been a problem to me.