From a engineering point of view, I worked on boeings for years and then switched to the Airbus 300/330/340's , yes it was a head twister, once you get used the switches being installed upside down and pulling CB's to fix 90% of problems your right.
Overall finish on parts of the Airbus aircraft you interface with everyday seem to better thought out and user freindly, and of slightly better quality. Once you dig deeper into the systems and structure designs you find it to be slightly lacking what the boeing has in the way of layout design and accessability.
The Airbus is also still experiencing operational problems boeing dealt with and resolved years ago. I am now am working back on the Boeing 777-200/300 and ER. Systems have been simplified dramitically over the Airbus especially 340-500/600. And seems to be a bullet proof machine out of the box.
Airlines are seeing a never seen before 3 year teething after manufacture to smooth all defects out, compared to 7 years for 330 and 8 years for 340, on average. Airlines on average took a 11 years to remove all teething problems out of the 747.
For 4 engines or 2? Airlines and engineers will always go for two, Easier to manage, less fuel burn, drag and weight, less structural stress loads, less spare parts to require, less maintenance, can I stop now, or I can keep going. AND YES SHE WON'T GO SPLASH, SHE WILL GET THERE!
I know for ground staff and ticketing they prefer the 330/340 y class seating config at 2-4-2 over 777 2-5-2 for group/family seating arrangement which can cause problems.
Hope that helps in a small way, if you ask me, I love the cockpit layout in the bus and the great ideas they have come up with, but I would still take the triple for better performance and reliability.
For effiency the pick of the bunch at this time for best all round would have to be A330 and B777. Leave the 340 at factory! its a head case!