If 2 engines weren't more efficient, the B777 wouldn't be the most popular plane for int'l airlines. There are no 3-engine airliners anymore and the A380 is certainly the last 4-engine design we'll see.
Dassault tried to claim that 2 was for "domestic" use and 3 was for overwater--worked until DA2000 customers wanted more range to go overwater.
GF