What is the difference in harmonic contents for amplifiers with and without negative feedback?

Amplifier`s with negative feed have less harmonic content in their output than those without.  Anything that prevents an amplifier from operating linear throughout a complete input cycle will cause the amplifier to generate harmonics in the amplifier`s output. Negative feed back along with a proper fixed bias keeps an amplifier operating within the linear portion of the amplifier`s operating range and thus prevents it from generating harmonics in it`s output.

Amplifiers with negative feed back have less gain but they are much less prone to go in to spurious oscillations which also cause harmonic distortion in the amplifier`s output.