I think it would be easier to make the connection still in Europe. If not Europe, than an airport that's not as busy as
JFK. I would probably feel more comfortable with a longer transit time there, but if that is what
DL sells then I would assume it's doable. Regardless of the transit time, I would be a bit concerned with delays at
JFK that time of the day. I don't think I've ever seen the block time of any NYC-
PHL flight that high. I usually see somewhere between 55 minutes and 1 hour 5 minutes. Without traffic, you could drive to
PHL in less than two hours.
IIRC, it's a bit of a walk between national and international flights in
MAD. Four hours seems like more than enough time for a smooth transition, if not a bit much. I've seen a lot of booked US-JK codeshare connections so I'm sure it's smooth. I don't know their locations in
BCN relative to one another.
US 762's are a bit tired, with no AVOD in coach. The seats are pretty comfortable though. Transatlantic in the 762, I've always sat in C. I did sit in Y for 4 1/2 - 5 hours and didn't find it uncomfortable. I sat in the middle without someone next to me and just slumped over.

The A333 is not bad in Y, and it has AVOD to keep you entertained. I am more of a reader if I am not drinking while flying (ie if I am not flying in a premium cabin!) so AVOD doesn't matter too much to me. I find both of these aircraft to be preferable to any 752 in Y for 8.5 hours!
The last time I flew transatlantic on
DL was in '05, and it was on the 767 in Y. I found it comparable to US transatlantic. I have never been on a
DL 752 across the pond, nor have I taken a flight more recently to be able to comment on their transatlantic service. I hope to take one this summer so I can update my opinion!
I would say that
AF's transatlantic product is superior to both
DL and US, although I haven't taken
AF since around the time of my last
DL flight. I would definitely check and see if the
UX flight and
AF flights are close in proximity.
CDG can be a bit of a maze! I do enjoy the airport, though, even if some others don't.
There are pro's and con's to all of your possible itineraries! Hope I helped at least give you some more information that will make it a bit easier to make your decision.
