Water, healthy oils, physical activity, fiber are all helpful for regularity.

There's nothing wrong with magnesium oxide if it works well for your goals/purposes for using it. It is less bioavailable however.

BeyondTheRainbow, you make a good point, some people cannot tolerate the citrate form without loose stools. Others need the citrate form. it's great the oxide formula helps your migraines.

Formulations, other than oxide, are generally considered more therpeutic.
Various formulations tend to target various conditions.

There are several formulations, each of which seem to best target specific purposes. This can be confusing. I solve this by using a formulation which has more than one type of magnesium in it.

There are formulations which have appox. 5 formulations of calcium and 5 formulations of magnesium. Example: Country Life's Target-Mins Calcium Magnesium Complex. I often use this formulation.

Country life also offers a magnesium supplement with multiple forms of magnesium, also referred toas "Target-Mins."