The A380 is far more comfortable in Y for lots of reasons, including greater pressurization (5000 feet vs 7000 feet for all other airliners until the B787 comes into service), higher humidity (so your skin doesn't dry out as much), and less noise/vibration. QF Y cabin and seating is well done with new technology seats, so more comfortable than QF 747 or UA (DL and Virgin might have the same type of seating, not sure). Generally UA is the cheapest (by far; and outside of the Twitter sales often has consolidator fares readily available) while QF is the most expensive. E+ on UA really cannot compare with QF A380 for comfort, so UA is worthwhile only if you can upgrade.