[Agema]

Don't underestimate Sermon of Courage. You can lose a huge amount of troops when you rout (especially if they're slower than your enemies) so in a close fight that morale boost can really make a difference. If you need to sort out a Dom problem H2 is much better than H1. I'm not 100% sure on this, but I think H2 mages casting bless and banish have larger AoE and maybe in the case of banish more damage, which makes them much more efficient.

Generally you wouldn't go out of your way to make H1 or H2 a prophet - you should make prophets according to other reasons (e.g. a high HP friendly Dom thug, a flier for more manoueverability). H3 might be worthwhile because they become H4 when made a prophet.

Many times you'll get H2 on a unit you actually want for other reasons (e.g. they're mage priests like Pythium's theurgs, or have a patrol bonus, etc.). If you are specifically recruiting a priest for the sake of it, bear in mind that you're detracting from you recruiting something more useful, as most people may only have temples in their castle provinces. Even if the two H1s are cheaper, it's an extra turn spent building a priest when you could have a mage, thug or whatever.