That primarily depends on your hardness. If it is very high, high-dose chemical treatment will lower the pH (never done it this way, I'd stay away from it). If your water is too hard, the pH is most likely not the only problem you face when you keep fish that want pH 7. In that case, you may want to consider an R/O unit to dilute your tap water, which will lower hardness and allows easier adjustment of the pH value.
Generally, peat is used to lower the pH value, however, the harder the water is, the more peat you need. Furthermore, it colors your water brownish. If your water is medium to soft, peat is the best way to go
Bottom line: It depends on what fish you keep, what looks you want for your tank water, and what hardness you water is.
HarleyK