For stereo use, mostly M/S with an omni mid. I suppose two coincident omnis may be useful for some close-mic'ing applications, but not for what we are doing. Angled apart (probably 90 to 180 degrees) doing so may be useful as a way to introduce a touch of stereo "air" and interest into an otherwise predominantly monophonic track. Could be useful for a vocals or a solo instrument.
For single channel use the omni position is of course useful as a single omni, or one could record both omni and 8 with both caps pointed in the same direction and combine them later in varying degrees and polarities to produce any 1st order pattern. You only get one channel output by doing that, but gain the advantage of dialing in any pattern with the ability to change it while listening later. Likewise one can cut that full range of adjustment in half by recording cardioid and 8, or cardioid and omni, to matrix later and dial in patterns between the two.