The argument over four engines versus two has been settled in favor of two -- provided that the two are robust and reliable newer model engines, and in an aircraft with modern fly by wire computer control systems that can smoothly adjust for the loss of a single engine.
The loss of both engines is another matter. When that happens, as when US Airways Flight 1549 ditched in the Hudson without loss of life, it helps to have a supremely capable pilot in command.
A 747 can fly with two engines out, but a first rate flight crew had better be aboard -- and you should prefer that it is one of the later models with a computerized glass cockpit.
If not, that flight crew will be hard pressed to work an older 747's essentially mechanical (if hydraulically assisted) flight controls and keep watch on its banks of old style gauges. For that reason, older 747s require a flight crew of three, as opposed to the two needed for modern twin engine airliners -- a potent consideration in favor of such twins for cost-paring airline operators.
Simply from a stability standpoint, 1 engine gone on a 2-engine leaves one side rather unstable. Whereas on a 4-engine, ther is still 1 on that side to continue. Much more stable by nature.
The 2-engine is understandable from economy standpoint, but everything else being the same, it simply is mechanically unstable if just 1 goes out of 2.