so i vote for Brown Sugar b/c it was the first i remember being hit w/the label.

but w/o regard for labeling i'd say Tony Toni Tone's Sons of Soul was the 1st. or at least the 1st i heard that was consciously evoking the sound and general feeling of 70s R&B/Soul w/minimal Hip-Hop aesthetic, as opposed to New Jack Swing and Hip-Hop Soul each of which had a heavier H-H influence and aesthetic.