I don't think there's a 788 economy class seating thread (yet, or at least one I can find), but this from the well-respected Dallas Morning News aviation columnist, Terry Maxon, caught my eye:
Don’t tell anyone, but I think the coach seating in Southwest Airlines’ Boeing 737-300s is more roomy/comfortable than the coach seating in American Airlines’ Boeing 787s.
Ouch!
Source: http://aviationblog.dallasnews.com/2...iday-220.html/