Both have such a large number of variations that there are very few players who play both as Black. I play Grünfeld as Black sometimes, but have only watched KID games. Both seem to be very good openings, but Grünfeld is more about piece activity against White's pawn center while in KID the center can be closed. In Grünfeld activity is essential, a couple of passive moves from either side can be decisive. The side who understands the position better, has the advantage. That of course applies to any opening, but in Grünfeld the punishment comes quickly.
is Grunfeld better than KID?
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It is generally agreed apon that the Grunfeld is more theoretically sound than the KID. But harder to play- not recommended for weaker players
Really? I would've guessed the opposite.
The KID looks extremely complex to me. A lot of positional maneuvering, in many of the closed-center lines, where White adjusts and expands with a queenside attack, while Black arranges his own expansion and assault on the kingside.
Whereas the Grunfeld looks more like the Modern Defense to me . . . very direct and straightforward in nature, bluntly pressuring and attacking White's central pawns, with that Bg7 knifing down that dark diagonal.
(I'm a QGD player, so I'm admittedly not well versed in either of those defenses. Though I've always thought that the Grunfeld looks "easier" to play than the KID.)
I don't know much about either, which is why I had hoped someone who plays those 2 will say something about both openings.
That being said,a few months ago, I watched one of IM John Bartholomew's standard games and he was playing Grunfeld. He stated that Grunfeld is extremely tricky to play because if you slightly mess up the move order you will be in a world of pain (and if I remember correctly he ended up having problems in the said game for the exact reason).