Off the top of my head, the first 15 or so rows are generally the older, blue leather style seats (with more substantial arm rests) while the rest of the seats are a newer style.

The newer style feels a bit more cramped to me, but I'm sure someone will be along shortly to confirm. Also, remember to pick a seat that exists in CW on a 747 - just on the off chance the aircraft is switched due to maintenance.

Source; 3-4 domestic 767 flights per month.