Here the relative pronoun which has two possible antecedents, either the noun angels or the whole clause itself. In his editing for the 1837 edition, Joseph Smith interpreted the which as referring to the angels; thus he grammatically emended the which to who. (The original text generally used which to refer to people as well as things; see the discussion under which in volume 3.) But one could also interpret the which here as referring to the act itself of sending angels to converse with men, an act that causes men to behold God’s glory, as is implied, for instance, in Luke 2:9: “and lo the angel of the Lord came upon them and the glory of the Lord shone round about them”. Technically, the critical text does not need to decide which meaning of which is intended here in Alma 12:29 since the original which will be restored. For additional discussion, see under which in volume 3.
Summary: Restore the original which in Alma 12:29, the earliest reading; the which here may refer to the entire preceding clause rather than to the noun angels.