Prefer(Sodium R-Lipoate). It is currently the most stable, most bioavailable, and most potent form available. Alternatively, look for R-Dihydrolipoic Acid (R-DHLA). It is the reduced form of R-Lipoic Acid (R-LA), the active R(+) enantiomer or eutomer of (Alpha) Lipoc Acid. Oxidization of R-LA produces R-DHLA, making R-LA and R-DHLA a so-called redox couple. However, most of the important properties of R-LA are due to R-DHLA.
The regular, racemic form containing both the R(+) (R-Lipoic Acid) and S(-) (S-Lipoic Acid) enantiomers in a 50/50 ratio is the least desirable form.