Which combo do you prefer and why?

1. QID/NID

2. KID/Grunfeld indian

3. Benoni d./benko

I would say QID/NID is a combo, but the KID vs Grunfeld is not a like.. Grunfeld is the most open Indian IMO

QID/NID is almost a required combination, as most Nimzo players will go for the QID if White avoids the Nimzo with 3 Nf3 - although there are other possibilities, such as the Bogo-indian, going back into the QGD (the Orthodox complex is a bit easier for Black when White no long has the option of Nge2), or going into the Modern Benoni with 3 ...c5.

Except for the Benoni, in fact, all those systems share some similar ideas and pawn structures in many lines, and many Nimzo players feel as perfectly comfortable playing the Bogo or QGD Tartakower as the QID.

The KID and Grunfeld are completely different.  Both have ...Nf6, ...g6 and ...Bg7, but the similarity ends soon after.  The Grunfeld explodes the center, forgetting about trying to maintain a pawn center and instead relying on sharp piece play to pressure White.  Black tries early on to maximize the scope of his Bg7, which often plays a key role.

In the KID, Black tries to keep a pawn center, which usually results in a closed position, preferring to mount a Kingside attack - often behind a pawn storm.  The role of the Bg7 is much reduced, and it is often Black's least effective piece because of the blocked center with his own pawn at e5.

Of course the Benoni and Benko are related by the pawn center, but the Modern Benoni most often involves an early exchange with ...e6xd5 and c4xd5, which gives Black the open e-file for his counterplay.  The Benko gives up a pawn to open files on the Queenside, so again the main similarity is the Bg7 position, although in this case it plays a strong role in both defenses.