The first one, which includes both Epsom salts and magnesium chloride hexahydrate, is the better option although the magnesium chloride hexahydrate can be a bit harder to find.
The following is an extract from the article linked to in Post 1
Residue Remaining from Recipe #1 when using Recipe #1, Part 3A
After one year of adding 8 ppm of calcium and the accompanying 0.4 meq/L (1.1 dKH) of alkalinity per day (41 mL of both parts per day or 4 gallons of both parts per year in a 50-gallon aquarium, including the effect of the magnesium part #3A, 2440 mL/year), the following residue (Table 2) would remain after calcification and adjustment for salinity (there is roughly a 32% rise in salinity over a year using this addition rate without water changes).
Note that in this recipe, all of the ions match NSW fairly closely (green), but without using Part 3A, the magnesium and sulfate are severely depleted (red).
Residue Remaining from Recipe #1 when using Recipe #1, Part 3B
After one year of adding 8 ppm of calcium and the accompanying 0.4 meq/L (1.1 dKH) of alkalinity per day (41 mL of both parts per day or 4 gallons of both parts per year in a 50-gallon aquarium, including the effect of the magnesium sulfate solution, 2440 mL/year), the following residue (Table 3) would remain after calcification and adjustment for salinity (there is roughly a 29% rise in salinity over a year using this addition rate without water changes):
Note that in this recipe, all of the ions except sulfate (red) match NSW fairly closely (green), but without using Part 3A, magnesium and sulfate are severely depleted (red).
Table 3. Elements present after one year of additions of Recipe #1, using Part 3B a
Sulfate is the main element which builds up to unacceptable levels by using Part 3B, although this can be mitigated by regular water changes.