My own personal experience for US-Europe long haul flights I've taken:
AA: Terrible. Bad food. Expensive alcoholic drinks. Overhead TVs and no personal entertainment- and ones that don't even work properly at that, pay for headphones, RUDE flight attendants, baggage allowance pretty standard, decent leg room at least, usually cheap(er)
BA: Nice food, nice flight attendants, good entertainment- usually the ones you can pause so you can get up and walk about and still hit the same point in the film, free drinks, snack, baggage allowance pretty standard, adequate leg room
Air France: Nice food, very good baggage allowance, good entertainment, free drinks, decent leg room- as long as you're not stuck in the middle seats in the plane. However, Charles de Gaulle Airport is awful!!
United (been a while, as I was turned off…) Overhead entertainment, last time I couldn’t even see the TV at all, so that was awful, crammed in like sardines, food- not great at all-pretty sure last time I flew them, alcoholic drinks were free… standard baggage allowance
Virgin Atlantic – ahh, my favourite, but I am biased because I have elite status. My work flights are Upperclass, but even in economy, I like them –nice entertainment, good food, free drinks, helpful flight attendants, (and the other elite status perks even in economy- the Virgin Lounge!!!, Champagne on the flight, the Revivals Lounge, extra baggage) - standard baggage allowance, leg room isn’t great though.
Hence why I said above, it’s all based upon personal experience ;-)