I usually use magnesium citrate. Magnesium ascorbate(magnesium bound to vitamin c) is also well absorbed. I suggest that you avoid magnesium sulfate as it is probably not so well absorbed. Taking 500 mg a day of magnesium in the form of supplements might be a good idea if you feel your diet contains little magnesium. if you do think you get significant magnesium in your diet then 250 mg a day of supplementation would be good.