Usually I leave it at the default which is Balanced or maybe up a notch to Better using the Intel encoder and MPEG4.
I have done tests with Best and worst (Fastest) and if you original footage is clean with little noise the difference is undetectable and the speed of encoding varies little. The difference in the settings affects how far in the frame the encoder searches for matching blocks of pixels in the compression process and this has a diminishing rate of return if the footage is noisy or has blurred detail.
With the Mainconept MPEG2 encoder I always left it at the default set by Magix as pushing it to max gave worse results at times.