I did BRU-ORD a couple of times on the old AA planes which was horrible. Both seating and food at that time was not good. Cabin Crew was very attentive and did their best.
I've also done YUL-LHR on BA recently on a 777 and this wasn't good either in economy.
Best flight long haul for me so far was LHR-DFW on AA on the new 777-300ER with 3-4-3. Even in economy I thought the seats were OK, IFE was excellent, staff was friendly and food was decent enough. Furthermore the inflight wifi was faster than my business broadband by BT (ugh) so I was very productive with catching up on work during the flight.
Next up is JFK-LHR on the 777-300ER with AA in Main Cabin Extra so can't compare that yet but what I've researched looks promising. It's not Business Class but for the fare that I paid MCE seems like a steal.
If I plan a next trip across the pond in Y it's either AA on the 777-300ER with Wifi or BA A380 just because of the plane and I've never had the opportunity to fly the A380.