The Now magnesium malate used to be a favorite but then they added calcium, which reduses its effect.
It was a big difference for me to get hold of a magnesium supplement without binders, fillers, calcium, coating, stearic acid etc.
Much more effective. I am doing fine on 2-400 mg of magnesium. This has for me been the single most difficult supplement to find out of.
I would up until bowel tolerance just to know where my limits was, same as vit C.
To maximize the uptake and utilization of magnesium; vit B6 are needed, so are boron.