Magnesium L-Threonate - has the most potent therapeutical effect because it can effortlessly cross blood-brain barrier. The drawback is that some people are sensitive to this form of magnesium, those people can have nausea, vomit, migraines, etc. IMHO, I would advise against everyday use because this form is more a medication than a supplement. It is used for serious conditions like dementia, neurological impairment, nutrimental deficiencies.

Magnesium Taurate - a combination of magnesium and taurine. A good form for people with metabolic conditions: T1DM, T2DM, hyperlipidemia, vitamin and mineral deficiencies.

Magnesium Glycinate (aka Magnesium Bisglycinate) - a bit less potent form of magnesium, but has good bioavailability, fewer side-effects. This form is also a source of glycine which is an important amino acid beneficial for metabolism, has a mild calming and stabilizing effect on nervous system. Helps to cope with anxiety, panic attacks, insomnia.

Magnesium Citrate - a cheaper but ok magnesium form for everyday use.

Magnesium Oxide - the cheapest and the least efficient form of magnesium. Unfortunately, this is the most widespread form in many countries due to its low price. Try to avoid this form if you have a choice.

Bonus point: if you have a specific condition, you can combine several forms of magnesium to reach multiple therapeutic goals. For example, some popular combinations are presented below:

  a. Magnesium Taurate + Magnesium Glycinate
  b. Magnesium L-Threonate + Magnesium Taurate
  c. Magnesium L-Threonate + Magnesium Taurate + Magnesium Glycinate