1977 5.1 and 1977 stereo are very similar. If you have only a stereo system, the stereo version will likely sound a bit clearer due to lack of mixdown, otherwise I prefer the 5.1 mix.

1977 mono mix is another favorite here. It has many interesting differences from the other 1977 mixes, but the audio quality is not as good.

1985 is, in a lot of ways, a merger of the differences in the 1977 mixes. It sounds okay but there's no dynamic range to speak of.

1993 is a good-sounding mix overall, and like the 1985 mix, merges together elements from the different 1977 mixes. But it's often criticized for including sound effects that were not original audio, so it's not as authentic.

Hope that helps.