Which shall i choose?

Ps i'm opportunist and got no morals.

Black Star is the "better" choice.

Azuras Star can only capture white souls.
Black Star can capture white and black souls even though the game suggests otherwise with dialogue.

The Black Star is much better.

thanks

In the end both store grand souls and there is no difference benefitwise. Finding humanoids to store in Black Star maybe less time consuming. However after a certain point it didnt matter, at least for me as all vendors were selling filled grand soul gems and money wasnt an issue.

Ah, this whole time I was under the impression that it could only capture black souls. This is useful information!

Even if it could only capture black souls, the Black Star is the better choice. Half the enemies in the game are human, getting black soul gems for them is very difficult.