[thejeff]

Blood 9: Chance (MR resisted) of cursing the whoever kills the blessed unit. Not very useful.

Death 9: It's an extra 2AN damage.

Earth 9: Not quite so clear. It's actually +4 to Armor, not natural armor. Only applies if armor is worn and may be less if the unit has more natural armor or if no helmet is worn. Also abusable using trinkets with armor value.

Fire 9: I think it was 8 in Dom2 and 6 now. Not sure. Don't have the game in front of me.
Generally considered the best, with Water a close second.