It's an important question for me, because I will not under any circumstances, use the tadpoles or their powers, but will be extremely angry if this choice results in Larian screwing me over on the trade-off because clearly the gains from using the powers are a very big deal. It would be especially egregious if the good/best outcomes of the game are possible to achieve only by using the tadpole powers.
I'm not sure that this is a game with a 'best' ending. It seems more like a 'best ending for you' type of game. Maybe turning into a half-mindflayer demigod is the best ending for you, or maybe removing the tadpoles, mindflayers, and absolute from the surface of the material plane is the best ending. Maybe they are all great and you should play through a couple times to see the variations.
