The front EC coach section on DL's 767 is quite nice (for coach). I've never spied an AF long haul economy cabin except front Premium Voyageur part, which are actually better seats than the economy seats in the back.

For the sake of completeness, I'll give a biz-class comparison:

This year, I've flown AF's 777 on the LAX-CDG route, and AF's A380 on JNB-CDG both in biz class. Of the two, the A380 is clearly the better seat.

I've also flown DL's 777's "herringbone" seat configuration and DL's "old school" 767, both in biz class.

Talking about the seats, DL's 767 and AF's 777 are both weak products. DL's because the seats are old and tired. AF's because they are shoe-horned in rows 2-3-2 across.

DL's herringbone and AF's A380 biz seats are both way better than the above two. I like both.

AF's food and wine easily beats DL in biz class.

In either class, who has the nicer FA's between AF and DL is an entirely random matter. I've met both great and mediocre on both airlines across the Atlantic.