What's the best response for white in the Sicilian Defense?

2.Nf3 and 3.d4 against everything but a6, b5, d5, e5, f5, g5, h6, and Nf6.

I think the ideal combination of objective merit and practicality is the Bb5 stuff, but obviously that doesn't suit everyone's tastes.

Great advice guys. The only point that is missing is that below 2000 ratings players who essay the open Sicilian as white will lose many MANY games through facing prepared opponents. Yes you will learn a lot, but at least read a copy of Nunn's Beating the Sicilian before you even think about it. That will show the sheer volume of defenses black has in answer to 2.Nf3 & 3.d4

Lastly, black WANTS you to play 2.Nf3 & 3.d4

I hate it when white plays 2.c3, 2.Nc3 with 3.g3 or 3.f4... It gets me into THEIR game instead of my own game. - something to think about.

To the OP, I used to have trouble too but not anymore.  What I do is play sicilian myself and learn from my opponent.  i play the same line as black which gives me a lot of trouble when playing white, see what my opponent does.  If my opponent has a good idea, I absorb it as my own.  Nowadays I am comfortable with sicilian enough that I don't play it as black anymore. 

I choose lines that has less theory.  the user above mentioned grand prix attack.  It's a good one.  but I think open sicilian is better.  I also play rossolimo and king's indian attack if black allows it.  If black plays dragon, I am very happy to play yugoslavian attack.

Ok but this stuff only works on 1.e4 c5 2.Nf3 Nc6 and 2...d6 sicilians.

U will have to chose something on 2...e6, 2...a6, 2...g6, 2...Nf6, 2...b6

Theoretically the Open Sicilian is White's best try. White has a small advantage going in, but the nature of it allows Black strong activity, so things can get wild. That's why the Sicilian is so common and considered Black's best response to 1.e4.

1.e4 c5 2.Nf3 Nc6 3.d4

There are lots of really good variations at this point. It's mostly highly theoretical.

You could also try the Smith-Morra Gambit, which is not considered completely sound anymore, or the C3 Siclian, which is more positional approach.

Black's best response to 1.e4?

Best response to 1. e4: 1.. e6!!! White resigns

Play KIA...

it is just an improved french defence for black, the Bc8 can be developped on g4 after Nf3 for instance...

3 g3/d3, 3 c3, 3 Bc4, 3 e5 Nd5 4 g3, 3 d4

Personally, aside from 2...e6, I've yet to meet any of the above in a serious game (although I'm sure I'll get a 2...g6 soon)

"... There is no doubt in my mind that if you really want to test the Sicilian then you have to play the main lines of the Open Sicilian. The problem is that there are just so many of them ... and keeping up with developments in all of them is a substantial task. ... as you become older, with other demands on your time (family, job, etc.) then it becomes more and more difficult to keep up with everything. At this stage it may make sense to reduce your theoretical overhead by adopting one of the 'lesser' lines against the Sicilian: 2 c3, or the Closed Sicilian, or lines with Bb5. ..." - GM John Nunn in part of a 2005 book where he discussed a 1994 game in which he had played 2 c3.

I've played the Open Sicilian, the Closed, the Grand Prix, the Rossolimo / Moscow, the Kopec system, the Alapin, the Smith-Morra, the Big Clamp, 2.a3 and 2.b3, without really being comfortable with any of them. Finally found this YouTube piece by Grant Szuveges on transposing to the Botvinnik English, and I really like it. White's first half-dozen moves are the same every time, the position is fairly closed so no sharp tactics in the opening, then White can choose from plans on kingside, queenside and in the centre. Every game I've played with it has been interesting. 

FrogCDE: 1.e4 c5 2. c4. I like it!

I think I read about the Botvinnik-English once and forgot about it. Botvinnik did like those pawn prongs like c4/d3/e4 or d5/e6/f5 in the Dutch.

Is there a technical word for those pawn formations?

c4-d3-e4 => Botvinnik structure

d5-e6-f5 => Stonewall structure

Both can be played reversed (for the Botvinnik, u can play it versus english).

I thought there might be a general term like "prong" which would cover V-like pawns, but good enough.

2.c3 (Alapin), is the best response.

I've been experimenting with 2. Qh5 lately. Having moderate success. The Siclian is quite a solid defense for black. I don't think there's a "trump card" against it.

As a Sicilian player with Black, I find the Alapin Sicilian most annoying. I seek to play the Paulsen or Taimanov Sicilian w early e6, so you can't play a Bb5 Sicilian against it. With the Alapin, White is trying to limit your counterplay and just get a lingering small positional advantage. The best defense for Black is played like the Alekhine defense, Nf6 allowing e5, which I really don't like.

With White, you can always play the Alapin if you are patient and don't expect to blast your opponent off the board in 15-20 moves. In the open Sicilians, Black can try a variety of complex structures. You'd get a bigger advantage with white if you know exactly what to do and have great attacking skills, but it takes a lot more know how.

The most comprehensive opening guide to the Alapin was written by Murray Chandler. GM Sveshnikov also played it with success and has written about it.

I breathe a sigh of relief when somebody tries the Grand Prix Attack. The defense is not that complicated. I know how the easy cookbook mating attack with Bc4 works, so I don't just walk into it. To surprise the Black player, you need some very unorthodox weirdness like 2 b3 or 2 Na3 or 2 g3, but that just forces Black to think for himself early and not rely on memory or habit.