Googling this question gave me only confusion, so here goes:

Polytheism gives +6 faith on Main Plaza. Shamanism gives +2 per MP and +3 per Administrative Center (outpost or absorbed outpost). Seems simple and obvious that if you have at 2-5 outposts and one city, Shamanism will be crushing it for faith generation. But some people were saying that it depends on if you have mountains or forests. Others talked about population being important. What am I missing?