nimzo-indian vs the gruenfeld

I know there's nothing similar about these two openings but I enjoy playing them both but if I should put serious time into learning one of these which should it be?

The Grunfeld is very sharp and theory-heavy, so if you have many many hours and a sharp memory, go for it. Otherwise, stick with the Nimzo.

Is their a certain book that would provide me with all the grunfeld theory?

There are two volumes on the Grunfeld by Boris Avrukh which are supposed to be very good. I've ordered them for my own library, but they're still shipping and so I can't make them a specific recommendation - I suggest you go read some of the reviews out there about them first.

sweet deal, I'll check them out. Thanks!!

Problem with the Nimzo Indian though is that you will have to learn something like the Queens Indian or the Bogo Indian along with it.

Can't white avoid a grunfeld with Nf3 I think. If I learn the grenfeld is there other openings I should familiarize myself with?

Yes, the King's Indian Defense is also good to know.

This is just a matter of taste!