I did the same with this mommy monster Aglepci, I chose the power and with the eye that the shopkeeper gave me, she gives another reward for her son's eye, for now the best options are being power and skill, the MC's power triples drastically, I remember that I had 80 power and it went up to 113, the only skill that didn't go up much. I was at 30 and it went up to 36. Even so, these two options are being the best for now, I could be wrong too.
I mean, I've tried asking her about, the monsters, about Ella's goal and gods that monsters worship but I haven't seen anything else worth the effort right now. so power and skill are best option!
By the way, there is another thing that is biting me is the eye that the shopkeeper gave, could it be that it only served as a bargaining chip with Aglepci or for something else?!