Textures or materials?

Hello.
I’d like to optimize the performance of my game, and would like to know which one is better to change in runtime,
the texture of the material:
gameObject.renderer.material.SetTexture(“_MainTex”, myTexture);

or the material itself to another one?
gameObject.renderer.material = myMaterial;

And why?
Thank you.

Can anyone answer my question, please?