Asteros:

 

I personally don't see much difference between airlines in Economy class. I would like to be proven wrong, but the idea to fly alternative airlines based on price or timetable makes sense.

If you're a smallish person, then you may not notice much difference. If you're more generously proportioned, or sitting next to someone who's large(ish), you definitely will notice. 

Apart from JAL & ANA, as far as I know just about all airlines - including Air NZ - run their economy class seating in B787s 9-abreast, when JAL & ANA run 8-abreast as Boeing originally designed. Most airlines (incl AirNZ) also run economy class in their B777s as 10-abreast, instead of the 9-abreat that Boeing originally designed. The result is that the seats and aisles are 17" (~43cm) wide, or "pretty bloody skinny" as we Self Loading Cargo say.

It is possible to avoid this problem: you could fly Premium Economy but while comfy, this is pretty expensive, or you could just choose an airline running Airbus aircraft.
This is not an anti-Boeing thing, it's just that the Airbus aircraft are designed to be less squeezy in Economy:
  * The A330 & A340 are B787 competitors but run 8-abreast 18" (~45cm) seats
  * The A350 is a B787 / B777 competitor but runs 9-abreast 18" (~45cm) seats. Also the A350 is much quieter for passengers than the B777.
  * The incomparable A380 runs 10-abreast but the seats are a relatively luxurious 19" (~48cm) wide, and the economy class cabin is the most spacious and the quietest you can fly in.

You may not think that a couple of centimetres extra seat width would make much difference, but it actually does.