Efficiency is greatest when you can switch components full on or full off. This is possible with square wave inverters. Then the inefficiency is chiefly in the transformer(s).
However when you want sine waves...
then you must devise ways to operate components at in-between states of conduction, which dissipates power as heat, dropping efficiency...
Or store and release energy in capacitors/inductors...
Or switch multiple components on/off in PWM, and filter the pulses to create the sine curve.
As a rule, the more efficiency you want, the more time and effort the topology will require.