grunfeld can is an opening thats really dangerous if you dont know the theory. also white in a lot of cases is the one that selects which lines to go down. awesome opening but maybe not the best as a backup unless you have tons of time
QGA or Grunfeld?

I play those openings as white and I prefer to play the QGA. Grunfeld can get dangerous for white quickly.

I am trying to decide on whether I should play the QGA or the Grunfeld as my alternative to the Slav.
My other openings are against 1.e4: French, Caro-Kann, Petrov's, and Scandinavian
Against 1.d4: NID/QID, Slav(not the semi-slav),and Grunfeld or QGA?
What do you all suggest and why?
Slav. Why pick hyper modern openings like grunfeld when you evidently are playing classical as white? Slav is solid, easy to play and does not have a problem piece (like the semi-slav or the french; a side note: Why not play caro-kann instead of french? no bad bishop ftw).

Why not just play them all? Adding two more openings will do no harm. You have too many already. NID/QID, Slav, that's already too many. With only one defense you can select many sub-variations. If you want to find out which structure suits you better, try "different" structure, e.g KID/Gruendfeld, and see if you can perform better.
Slav, QGA and Gruendfeld are different. Without knowing your "skill" it is difficult to say which one is better for you.
I am trying to decide on whether I should play the QGA or the Grunfeld as my alternative to the Slav.
What do you all suggest and why?