I've flown this route on Delta, Qantas, Air Canada (via YVR) and United in economy before.
Delta, Qantas (747, not 380) and Air Canada were all fine. I am 6'4" and 250lbs. I was glad to get off the plane, to be sure, but it was totally fine. I preferred Delta's seats to be honest, they seemed squishier. AC was a close second.
I did not care for United Economy but scored a complimentary E+ upgrade which was good one time and business another (which was actually REALLY good).
There's my experience.