NZ is said to give you the most leg room (or at least seat pitch at 34") in economy. QF is a bit skimpier (31-32") but I find the seat recline and seat back rather comfortable.

I detest the shape and limited recline of the QF "Dreamtime" BC seats so advise that you avoid that. My GF flew NZ BC (her first BC experience) and found to substandard to US's (A330 and 762). UA may end up being the best.