How do you determine which is the most suitable IVTC setting to use in TMPGEnc?

Options are:

1) 24fps flicker prioritized
2) 24fps motion prioritized
3) 24fps non-interlace source

(plus a couple of others that I'm not interested in)

How do I know which is the most suitable and will produce the best result for my source? The Help says that flicker prioritized is the default, but non-interlaced seems to be selected automatically for the vast majority of (downloaded DivX/XviD) sources I use as input.

Is it best to always select flicker prioritized, or should I just leave the setting as what TMPGEnc decides is best based on the input?