I currently use magnesium oxide in a tablet form (I use half a tablet, ~125mg). I have previously used magnesium glycinate but I don't remember what dose I used of that.

I'll add, the mag oxide always prevents leg cramps when I take a full tablet (250mg) when I am working outside all day (and staying hydrated).

ETA: In my experience magnesium citrate is the one mostly likely to cause diarrhea though they all can.