Magnesium comes in quite a few forms and it is my opinion that everyone reacts quite differently to each form. Magnesium is critical in over 350 enzymes including immune, neurological, adrenal function and homeostasis. If you google Mildred Seelig (MD) and Chronic Fatigue Syndrome you will find an extensive article she published concerning the role of magnesium.
Magnesium chloride is a highly bioavailable form and has worked well for me, I have also used UltraMag which is a blend of magnesium. Malic acid never did a thing for me.
Magnesium can be a tricky mineral to utilize and is quite sensitive to a number of factors. Vitamin D status should be checked as well.