troll priest serve the loa, shaman serve elements and ancestor spirits.
This is open to interpretation. All trolls serve the Loa, to be honest (and the Loa are
ancestral spirits, in addition to primal elemental forces). I see almost no difference between troll priests and shamans, personally. If I had to point to some RP-distinction between the two, I'd say that shamans are servitors of the ancient, primordial spirits of the world (who are Loa), whereas priests are devotees to the animalistic Loa who are themselves
servants of those same spirits. A troll priest might worship Akil'zon, the Amani Eagle Loa, for example, but Akil'zon is an aspect of the great spirit of the Sky, which is what shamans communicate with.
Everyone's interpretation will be different, but for me, its:
Elemental Loa > Animalistic Loa > Trolls
But all trolls revere the Loa. Honestly, to me, its all just different shades of the same colour; I see basically no difference between troll priests and shamans in game terms.