The problem is it depends. Depends on the mode and the way the mix was done and how it interacts with the mode. Usually a stereo mode will work best, but some times a different mode might give more punch or sound better or be clearer.
That's the problem - the mode to use depends on the content being played - one movie might require stereo to sound best, while another movie a downmix sounds better. Which one to use depends, and it's one reason why they toss so many in. The only real way is to try a few of them and pick the best. (Once you test a few, you know which ones affect the sound the most and are the ones to try, while the other ones can fine tune it).
The modes are free to use, so there is no harm in testing them all.