There are two main ways of continuing after 1...c5 for black in the Sicilian: advancing the queen  pawn (2....d6) and developing the Queen-Knight (2....Nc6).  What are the advantages and disadvantages of each of these strategies?? 

I dont like Nc6 because Bb5 scores a a healthy win percentage for white.

And I prefer an aggressive e5 pawn push. 

All three main second moves are fine for Black. 2..d6 tends to lead to slightly sharper lines (Najdof/Dragon) while 2..Nc6 leads to the classical lines as well as Sveshnikov/Accelerated Dragon. So it is a matter of personal style. 2...e6 is also more positional (for a Sicilian) and I have also found (as White) hard to meet. All are good choices depends on how you plan on following up.

I play Bb5 against 2...Nc6 and 2...d6, though I've read that a lot of Sicilian players don't play 2...Nc6 in order to avoid it (I believe it was one of the reasons given for the Accelerated Dragon variation).

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No sound chess opening is UNBEATABLE, though.

 

I like 2...Nc6 because it keeps options open. d6 is also good because it keeps available what I think is one of the Sicilian's major unbalancing forces - early development of the Queen's Bishop. This is also why I don't like 2...e6, because then you've mixed your play with the French Defence and are preparing to respond in a way that doesn't seem thematic of the Sicilian (to me).

Does anyone know why there was a major shift from 2. Nc6 to 2. d6? Why do contemporary GMs prefer the latter move? 

According to a couple of databases, 2...d6 is more popular and scores slightly better. Any are perfectly acceptable, though. I think you should try out a few different variations and see which one fits your style.

I suggest you join http://www.chess.com/groups/view/the-sicilian-superstars if you want a good discussion place for the opening.

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 Thanks! I just did!

I like 2. ...d6 because it allows the Najdorf where Nc6 is not as valuable as Nbd7-c5, hitting the e pawn and the Sozin bishop, should it end up there.  Additionally, it gives me an extra move in the Shveshnikov variation.  Consider the following line:

 

 1. e4 c5 2. Nf3 Nc6 3. d4 cxd4  4. Nxd4 Nf6 5. Nc3 e5  6. Nb5 d6.  White's threat on move 6 is Nd6+, where the BxN is essentially forced.  So black must play ...d6 to bring the queen onto the defense of it.  White then has Bg5, pinning the knight to the queen.  That is important: 7. Bg5 a6 8. Na3 B5 threatens ...b4, forking the poor knights, so White plays Nd5 and chaos ensues. Black wants to play Bb7 to hit the knight and the pawn, but the c6 knight is in the way, and he has to defend his knight first with  Be7. 

Now consider 2...d6 instead:

Here, black has already played d6.   White can't get in Bg5, and so the knight on f6 is free to help control the weak d5 square.  ...a6 and ...b5, threatening the fork, are immediately playable and force the c3 knight to move away, either up to be traded/attacked or backwards in retreat.  What does black give up? Queen control of the Rook on a8, so grabbing the e4 pawn right away runs into difficulty on the long diagonal.  The pawn will fall in good time.

 

Note that the standard line, if one just looks at Black's moves w/ the queen knight involve: Nc6, Nb8, Nd7, then either Nf6 or Nc5 (hitting e4 either way)  This move difference saves those two tempo.  Why isn't it the main line?  Because White gets 3. Bb5, as already mentioned.

I prefer Nc6 because I play the Checkhover variation as white, and that's something I wouldn't ever want to defened against as black . (1.e4 c5 2.d6 d4 3.cxd4 Qxd4)

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 Maybe it is due to the trend back towards tactical playes with Kasparov becoming champion. d6 is sharper so the tacticals support it.

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Even without the diagrams, this post was very helpful, thanks.

 

It seems that d6's advantage is that it prevents the advance of e5, allows the Najdorf, and prevents the Magnus Smith trap by hitting on the Sozin bishop.

 

Thanks to all who commented, too!

I like Nc6 better because it is flexible, and I can decide whether to enter a Dragon style variation or not.

It all depends on the line you want to play if White follows up with 3.d4.

Najdorf: 2...d6

Dragon: 2...d6

Accelerated Dragon 2...Nc6

Scheveningen: 2...d6, 2...e6 or 2...Nc6

Sveshnikov: 2...Nc6 (or 2...e6 if White cooperates)

Four Knights: 2...Nc6 or 2...e6

Classical: 2...Nc6 or 2...d6

Taimanov: 2...Nc6 or 2...e6

Kalashnikov: 2...Nc6

Hyper Accelerated is 2...g6, O'Kelly is 2...a6.

(wonder if I forgot any important ones)

 

So the issues of possibly avoiding Bb5(+) only come into play if the Sicilian you want to play has some flexibility regarding the second move.

One can Enter the Dragon (just like Bruce Lee!) from d6 by transposition of moves.

i wish i have a board now.. to test all those interesting theories. Oh well..

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your move list doesn't make any sense whatever way you look at it...

This is a game in which Susan Polgar smashed Shirov with her pet variation of the Chekhover when Shirov played the d6 sicilian