Complex sentence: Some types of single-phase motors or synchronous motors advantageous in some situations can be used, but three-phase induction motors are usually generally preferred as the most economical motor choice.
Split into simpler sentences: Some types of single-phase motors can be used, but three-phase motors are usually preferred. Various types of synchronous motors offer advantages in some situations, but three-phase induction motors are suitable for most purposes and are generally the most economical motor choice.