Faith or redemption?

Edit: by redemption I mean heresy

So I've been wondering. The tech tree doesn't show exactly how good faith is, so it's hard to say which one would make more sense to have in a given situation. Do you people know, how it works?

The context: I enjoy Burmese. They have a problem with range. So elephants make sense with their extra pierce armor. Especially because Burmese don't get siege ram. But my opponents often mix in some monks. I guess that in this situation heresy would be better, because the elephants are so slow. The monks have plenty of time to convert regardless. But it's hard to say when there is no clear information.