Definitely BA.

~Guaranteed flat seat
~The "Z" position is *heaven* for lounging in with some tea, a scone, and a glass of bubbly.
~Acceptable food; above average drinks (Kir Royale...hic...)
~No complaints with IFE. There's enough content to suit most, though they do keep it generally wide-appealing (IE, few movies catered toward the low-end youth demographic that would probably offend most other pax)
~Cabins seem to be in decent shape. The J product is a few years old, but I've generally found it clean and well maintained. But again JFK-LHR is the route in the network. I would imagine that LAX birds would be similarly well treated, but I've heard some complaints about premium cabins on the (comparatively) lesser routes such as SFO and EWR.
~Generally a professional, interested, "genuine" service (at least on JFK-LHR)
~Comparatively stunning lounges that offer a premium experience (versus paying for drinks at an American lounge)
~Prompt handling of irrops/general screw ups that happen
~EU protection for when/if something really goes wrong.