Which creatures from the alternative upgrade options do you choose?

I wouldn't say that shamans are completely useless. Considering that they can slow down or speed up units by 30%, the effect can be quite significant. I always cast it on centaurs first, then on executioners/chieftains, and then depending on the situation. Maybe sacrifice a unit and cast magic again, or maybe send them into battle. There are also situations where a ranged unit needs to attack before the centaurs. You cast the slow spell on those ranged units, and the centaurs attack first (of course, if the initiative difference is small). I'm more inclined to use Daughters of the Earth. However, I don't hire them at the beginning of the game because they are too expensive; they are more useful from level 5 onwards.