I think the Queen method is more efficient from a logistical standpoint.
If you have an egg, it produces a facehugger which requires a host.
It seems more efficient for a Queen to lay these eggs than to waste potential hosts creating more eggs.
Say you had two rooms, each with ten people and one impregnated human in.
In the room where the aliens use egg-morphing, the alien bursts, matures, and turns five humans into eggs while the other five are used as hosts for the new eggs.
In the room with the queen method, the alien bursts, matures into a Queen. The Queen then lays ten eggs, each of which impregnates a human which produces an alien.
So, in short:
Eggmorphing: 5
Queen: 10
Though egg-morphing is a possible backup method to create a Queen if none exists, perhaps.