What's your go-to opening against 1.d4 as black?

I have been trying to improve my chess game as black against 1.d4, and I am not sure which opening to learn. I have been looking various options like the Grunfeld Defence, The modern defence, The Slav defence, the Nimzo-Indian defence, the Dutch defence and the King's Indian Defence, but I have yet to settle on one.

I am interested in hearing your opinions on the matter. Which opening do you think is the most effective against 1.d4 as black, and why? Have you had success with a particular opening in your own games?

I think there are a lot of dependencies:

1) What do you play against 1.e4?  French players, who master the blocked center, would do better with the Kings Indian.  Sicilian players, who tend to prefer a more dynamic center, would do better with most lines of the Nimzo.  Alekhine players, who like to fight the mobile central pawn mass, would do best going with the Grunfeld.  Caro-Kann players, who surrender the center early with dxe4 and holding a compact position would do best playing the Slav.  Your 1...e5 players tend to do best with declining the Queen's Gambit with 2...e6.  You have to look at your stylistic preferences, like Blocked vs Mobile vs Static vs Open vs Dynamic center.

2. Are you talking over the board and internet blitz, or correspondence, like ICCF, where computers are allowed.  Correspondence chess most will play the Nimzo-Indian because it tends to be the strongest with computer assistance, but with the human factor, there is a LOT to know, even more than the KID or Grunfeld.

Hope this helps.

@1

"which opening to learn" ++ Do not learn, just play and analyse your lost games.

"Grunfeld Defence" ++ Good, but hard to play correctly.

"The modern defence" ++ Not that good.

"The Slav defence" ++ Solid but passive.

"Nimzo-Indian defence" ++ Good, but you lose the bishop's pair.

"Dutch defence" ++ Not solid. See Figure 4 (a)

"King's Indian Defence" ++ Good to play for a win with black, but at greater risk of losing.

"the most effective against 1.d4 as black" ++ 1...d5

"why?" See Figure 30

Queen's Gambit Declined.

In your shoes I'd avoid the Grunfeld as too theoretical, the KID as too theoretical and too dangerous ( probably the most interesting and at the same time the least practical for non-professionals ), the Nimzo as it requires knowledge of pawn structures that are typically studied at higher ratings, the Dutch because the weather there sucks 😁, the modern because I don't see a point in playing it.

This leaves the QGD and the Slav complex, between the two I have a small personal preference for the QGD, you can also play 2-3 lines in the QGD complex depending on whether you want to play a dynamic or solid game.

I play a very sharp Sicilian Najdorf against 1. e4, and the King's Indian Defense against 1. d4

Too one-dimensional. I prefer openings that can reach a wide variety of middle-games, and explore a wide variety of plans.

In times long past I played KID,KID,KID,... .

Later modern (1. ... g6) vs almost everything. Had some great wins and crashing defeats with it. (Problem I had with the modern is that only Duncan Suttles can play like Duncan Suttles no matter how hard I wanted to.)

Then studied Spassky's games vs Petrosian and really liked the Tarrasch. Since coming back to chess after 40+ years I've focused on Tarrasch and it's been good so far.

But, ....... I learned A LOT in all those old KID games. That experience was very valuable.

There are different ways to play the KID. In the Panno, Black often attacks on the Q-side, not the K-side.

Yes.

If he plays 16. bxc5, then I first kick his Bishop back with 16. ... b4 before recapturing on c5.

This continuation (15. ... Nc6! intending to meet 16. bxc5 with 16. ... b4!) constitutes the refutation of White's Ba3 and b3-b4 idea. IMO.

The Panno variation (6. ... Nc6) is a bit odd in that it appears (in theory) that Black's c6-Knight should just get kicked to a bad square by White's d4-d5, with a massive advantage for White in both space and time... but in practice it doesn't seem to work out that way.

The Knight on a5 turns out to be surprisingly well placed.

Sicilian or the pirc defense. that's what i play

Keep It Simple for Black by Christof Sielecki...

https://www.amazon.com/Keep-Simple-Black-Straightforward-Repertoire/dp/9493257517/ref=sr_1_1?crid=DJF666KT94DS&keywords=keep+it+simple+for+black+chess&qid=1676561831&s=books&sprefix=keep+it+simple+for%2Cstripbooks%2C137&sr=1-1

https://www.newinchess.com/keep-it-simple-for-black-hardcover

https://www.newinchess.com/media/wysiwyg/product_pdf/9115.pdf

https://www.chessable.com/keep-it-simple-for-black/course/92793/

The Panno tends to work best in situations where White's c4-Pawn is undefended.

Then the continuation 7. d5 Na5 attacks the undefended c4-Pawn, so Black gains time to play c7-c5 saving his Knight from the threat of b2-b4 trapping it.

Another point about that game (above) that's worth noting is that Black was not afraid of the en-passent capture dxe6 because his great increase in piece activity after Bxe6 left White unable to exploit the weak Black Pawn at d6.

I like both King's Indian and Nimzo-Indian.

King's Indian is more daring and aggressive.

Nimzo-Indian is more solid and positional.

I play 1...Nf6, if white goes for the London with 2.Bf4, I transpose to d5 lines with 2...d5

If they play 2.c4 however, I play KID

Why in the world would you answer 1. d4 Nf6 2. Bf4 with 2. ... d5?

Why transpose back into a London when 2. ... g6 and a KID formation is so strong against Bf4?

If white plays a regular London System (e3, c3, Nd2) vs KID then it's good for black. However, this allows white the option of transposing into a favourable line of the Pirc with Nc3 and e4.

The reality is that this attack works out incredibly well for white so playing an early d5 or c5 is advisable.

After ONE more move, 5. ... Nc6 (playing it like a Panno, and intending to meet 6. d5 with 6. ... e5!, isn't this line good for Black? White's Bishop does not belong on f4 in this position.

Schmidt vs Botvinnik is an example.

The Pirc might not be quite equal for Black in games between 3000-rated engines, but in games between PEOPLE Black is scoring better than 50% against White's Bf4 Pirc.

I also like ... c6 and ...b5 (with ... a6 (not a5)) to follow, against White's Qd2 and 0-0-0 plan.

Buddapest Gambit

You can't play that vs D4...