I dislike Astarion, even from the first meeting during EA I disliked him. I keep him in camp, but don't enlist him except for 2 times. For the Cazador quest, cause I do want to allow him his revenge, and more importantly, to take him to Araj Oblodra (one of the side characters I like most of the game) to let him taste her blood. I think this is one of the funniest scenes in the game, and a valid reason to keep Astarion alive.

So when I enlist him to go visit her and he tells me "Darling, I thought you'd never ask". I have to smile and think, "if you knew what I have in store for you buddy".