I think Ancient Minerals Bath Flakes may be the best. I use it every day (4 heaping tablespoons for 30 mins) and have religiously for the last nine months. I notice the difference after 20 mins. Hotter water seems to help the Mg get absorbed better, but you need to be careful of course not to get burned.

Bath or foot soaks are better than supplements because they don't put your absorption at the mercy of your gut health. I have never noticed an energy boost after taking Mg supplements.

But I don't have time at the start of the day or middle of the day to soak for 20-30 mins, so I use supplements then. One doctor with a book out says only 15% of Mg supplements get absorbed.

The mistake most doctors or naturopaths make is to say take the Mg to the amount your body can tolerate without getting the runs. It makes more sense to fix your gut first and get the flora right. Once I did that, I was able to take 5-10 times more Vitamin-C, for example, and much more Mg, too.

Epsom salts may be as good as Ancient Minerals bath flakes. I haven't compared them. I just know what works for me and don't want to fix what isn't broken.

It's important to get your kidneys tested before taking lots of Mg.