That doesn't mean the Nimzo is not good, it's just better to play the SS if you like crazy chess
Nimzo Indian or Semi Slav for Repertoire Choice?
If you want to play aggressive chess I recommend you to play King's Indian Defense. White can't decline it like Benko Gambit, or White can't pick up "drawish" variation like Exchanged Slav. I could recommend you to play Budapest Gambit (not really sound opening) or Grunfeld Defense, or even Chigorin Defense, but these openings require knowledge of the QGD, because White can transform them into passive equal lines of QGD.
If you want to play aggressive chess I recommend you to play King's Indian Defense. White can't decline it like Benko Gambit, or White can't pick up "drawish" variation like Exchanged Slav. I could recommend you to play Budapest Gambit (not really sound opening) or Grunfeld Defense, or even Chigorin Defense, but these openings require knowledge of the QGD, because White can transform them into passive equal lines of QGD.
Yes white most certainly can play a drawish variation against the KID. Really if you want a "guaranteed" unbalanced game against 1.d4, you'll have to play the Modern Benoni, and even then white can play the London System or other sidelines.

@DaniilKalabukhov The problem with the King’s Indian, in my eyes, is that white has a plethora of lines to choose from, ranging from a Petrosian or a makogonov with with playing h3, to a main line bayonet, where black has to know at least 13 moves of theory to just survive the opening.
@DaniilKalabukhov The problem with the King’s Indian, in my eyes, is that white has a plethora of lines to choose from, ranging from a Petrosian or a makogonov with with playing h3, to a main line bayonet, where black has to know at least 13 moves of theory to just survive the opening.
The Semi-Slav is hardly much better after 5.Bg5.

Not as much theory as the kings Indian! For example, schandorff’s book on the semi Slav was 1 book, while kotronias wrote 7 books (I think) on the kings Indian alone! Keep in mind that all of these booms were published by quality chess....
There is more theory in the Dutch sidelines than in the actual main lines
Not if you play the French against 1.e4. Also the theory of the Dutch including sidelines is still less than Semi-Slav
If you play the Stonewall though you should probably learn the Hedgehog against 1.c4 and 1.Nf3 as the Stonewall doesn't work against these moves.
Honestly, the semi-slav is more active and complex; just take a look at this variations
n: