On the 777-300 and A350, at least, Air France has a very comfortable, very competitive Business seat. But the food and wine really are remarkable; cuisine is France's calling card, and Air France respects that. I've also had consistently polished, professional service on Air France; while I find Delta crews typically friendly and outgoing, it's nice to get the full European treatment.

That, and I think Delta's seats are hard enough to cut (literal) diamonds.

I'd choose AF.