Comparing the A340 and B777.
From what I have read (mostly on these forums), the A340 will burn a little less fuel on long haul flights. The difference is very small. Because the A340 is designed to be operated strictly as a long haul plane, it may well be true.
Regarding maintenance issues I would think the twin engined 777 would be cheaper.
Its a good question Donder10. It will be interesting to hear the responses of others who may have access to performance data of these a/c.
Certainly other factors will be considered. Routes, engines etc.
Thats all I know. However, I could be wrong!
A330-200 Vs B767-400.
Take a look at the site below, there is some technical data on these planes. It may help answer some of your questions.