@jc76 The magnesium citrate is probably the fastest absorbing but for some people it's too fast and it gives you the trots! I've taken it with no problems. Magnesium glycinate seems to be the top recommendation these days but it has a drawback too - the supplement itself is bigger so the capsules are bigger and you need to take three or four for a full 400mg dose, OTOH you may not even need to take the full dose because it's so efficiently absorbed. That's what I've been using recently, the last year or so.

With the basic magnesium oxide the 400mg of magnesium fits in one modest capsule, they say you absorb less than half of it but nobody seems to then suggest taking more. I've taken just the plain magnesium oxide, it seemed to help, but I've tried the fancier (and more expensive) versions anyway.