The First Chassidishe Sefer
Torah learning
Rav Yaakov Yosef of Skver used to say, "The first Chassidishe sefer is the Ohr HaChaim HaKodosh." He taught that every word in it is an entire body of Yiddishkeit, and that there is almost no Chassidus of which the Ohr HaChaim is not the bread and butter of its foundation. In his view it is the one sefer that has been accepted by the greatest number of chassidim.
Source: Be'or HaChaim, p. 241; Nachlas Tzvi Kovetz 7, p. 52