Grunfeld is better and changed in the last 30 years...
Playing what? The NimzoIndian Defense? The Nimzovitch Defense or the NimzoLarsen Attack? Or any one of a dozen or so Nimzovitch Variations not to mention the Advance and Winawer Variations in the French, both of which should also be named after him but aren't I guess because so many other variations are in the CKD, Sicilian, RL, Philidor etc. are.
I guess the question is about 1.e4 Nc6, the nimzowitch defense?
Players much stronger than myself play this regularly, so i guess it must be a respectable defense overall, but black has some practical problems. The main one is that as far as i know 2.Nf3 is a rather frustrating response. The recognized best move is 2...e5, but then why starting with 1...Nc6 to traspose to 1...e5? that would mean giving white extra options (2.d4) without having something (ok, you avoid a couple of respectable gambits) in return. Other moves have been tryed, but theoretically white is better.
If you are ready to meet 2.Nf3 with e5 (or if you think that you found another respectable option), then it's time to study 2.d4 d5, where black has to play with great precision but seems to get a playable game. It's not a defense for the faint-hearted, but you might score well with it after careful study, expecially since (as often happens for this sort of offbeat lines) published theory often contains mistakes and a "prepared" white player might rush right into an unexpected novelty.
Personally speaking 2.Nf3 always prevented me from adopting this defence, but there is nothing terribly wrong with it.
grunfeld is better. Lost track..but back again with muliple variations.
I highly recommend A Complete Defense for Black by Raymond Keene and Byron Jacobs. The book proposes a repertoire that is based upon playing 1...Nc6 against any first move by White.
After 1 e4 Nc6 2 Nf3, Keene and Jacobs recommend 2...d6.