I'm going to come down on the side of AA on this one. The AA fleet has largely been refreshed barring the left over fleet from US Airways which is also being refreshed. I mainly fly premium cabins and find the flight attendants welcoming and helpful and the seats comfortable. Long haul AA wins hands down as it has some of the best business class seats available. 10 years ago delta was ahead of the game but now their fleet has an odd selection of business class seats.

I recently flew Delta / Air France to South Africa and was underwhelmed by Delta. DFW-ATL was on a "vintage" MD-80 with no IFE. On my return CDG-ATL was serviced by a 767 with coffin seats so narrow that I could not lay flat on my back as my shoulders were pinned between the sides of the seat. I also had to use the rest room and as I was unfamiliar with the aircraft headed to the front of the plane. A cheerful flight attendant asked if I was going to the restroom and directed me to the back of the cabin telling me to ask the flight attendant that was in the process of beverage service to let me pass. I politely asked and was met with an angry face and an eye roll. Food was marginal on the flight as well. In addition the inbound flight was over 2 hours late arriving to Paris due to tech issues (old aircraft) so I missed my return connection in ATL. On deltas side they had proactively booked me on the next flight to DFW which was on a new A321. A very nice aircraft but as I was in 1A I had very little leg room.

So while AA does have some grumpy flight attendants I do feel they treat their elite and premium cabin passengers well and have an excellent fleet of long haul aircraft as well as a largely refreshed domestic product.