Looking for flights to NY in May, KLM is some E120 more expensive per person for the return flight JFK-AMS (party of 4) than the DL flight.
Opinions about DL flights TATL I heard haven't been very positive but how bad are they really compared to KL? Last time to NY (my first intercontinental) on KL was very pleasant with the IFE, food and seating. How does DL compare? How are the planes? I've heard about dirty old 757/767 flying JFK-AMS or are they refurbished recently? With or without PTV? Food is bad?
Also, this is sold as a KL flight (KL 6070) so what about the miles and Skyteam Elite perks? Are they always honored at JFK/with DL and what can I expect there?
BTW this flight departs at 16:20 and will arrive at 07:40, any chance of sleep or are the seats not comfortable at all. Also, outbound is on KLM metal.

I'd be grateful for any advice!