Which option should I choose from (SCREEN) in AC3 filters for the best result ?

I have 5.1 computer speakers, x-fi sound card. 80% of movies I watch are 446 Kb/s, 28KHz, 6 channels, AC3.

What are the differences between "3/2 +SW - 5.1 channels", "Dolby surround" and "dolby pro logic II" (in ac3 filters, not in general)