There's basically two aspects arising from your question:
Efficiency - fuel burnt vs. weight transported
Yield - money spent vs. money made
As for the second, it will be difficult to get correct answers. All operators work with very different set-ups of passenger distribution (F-C-Y) and cargo supplement. Additionally we do not know the price they pay for the aircraft in mortgage or leasing and peripheral cost like crewing etc.
It seems that there is no direct law telling us which aircraft yields better.
As for efficiency, this is easier to prove. Simply analyze flight plans with payload in kgs/lbs with same ESAD vs. burn.
It is instantly clear, that the modern two-holers like A333 and B77W come out as winners. This because nothing is lighter than a design with 2 engines on 2 lag struts.
Weight is burn with more or less similar technology in construction and propulsion. This is not my invention, but pure and simple physics.
There is not yet a possibility to compare the 748 with the A380 on similar routes with similar set-ups, therefore it is still hard to tell. I would guess they are similarly efficient, but both a long way behind the modern 2-holers.