Is this a general discussion or do you have specific routes in mind?
I ask because, in my experience, crowning a champion economy product does not help in the decision making process. One may compare 10-20 airlines flying transpacific but pricing, restrictions in routings (unless one is paying full fare) and scheduling considerations often narrow the field down to 2-3 candidates.
Assuming one is willing to pay full fare, fly at any hour of the day, connect through any airport etc., this becomes a general discussion (mostly for the fun of it IMHO). In this case, here is my very own subjective take on economy class inflight products:
MH is a pretty safe bet with comfy adjustable seats with personal screens and pitch at 33-34 in. throughout its transoceanic longhaul fleet. That said, I would choose SQ if I know I will end up on their B777 aircraft, because with slimmer seats (especially the older B777 seats), the legroom actually seems equal to that of MH despite the supposedly inferior pitch; plus I do actually prefer SQ's catering. Not having previously flown NH and looking at their advertised product (34 in. pitch and personal screens), I suspect they might be better than both SQ and MH in economy. If I could somehow plan a route that involves AC's A340-500, seat and IFE would be very good; except I may risk, based on hearsay, being faced with unresponsive cabin crew. Meanwhile, I could just as well go with UA if I had status that lands me in Economy Plus; adjustable seat with excellent legroom, decent catering, personal screen, AND Channel 9! Having just recently experienced the UA cabin crew for the first time on two transatlantics, I'd say cabin crew service is excellent or maybe I have been lucky. Nevertheless, if I feel I really want to rest, BR's very affordable Evergreen Deluxe is almost the only way to go, plus I love the congee they serve for breakfast. Finally, if I decide to splurge a little, I would definitely give SQ's Executive Economy a try.
I have found it difficult to be more conclusive than that.
