Sicilian Najdorf or Caro-Kann in a particular situation

First off, I am not asking whether the Sicilian Najdorf or the Caro-Kann is better.  Both can be good.  I am asking about the following:

Suppose I know both the Sicilian Najdorf and the Caro-Kann very well.  No additional opening study would be needed to "learn" either of the two openings.  I am playing in a tournament.

How do I decide when I should play the Sicilian Najdorf and when I should play the Caro-Kann?  Are there certain factors that would help me decide one way or another or should I just simply alternate between the two randomly?

Then, how come many GMs (Anand, etc.) play both?  And how do they choose which one to play in a particular game (which is what I was asking in the first place)?

Kramink used to play 1.Nf3, arguably to early discover plans of Blacks...

Logical would be to ecape from theory whenever you play someone who likes long lines ;)

Do you have any knowledge of what lines your opponents will play against you? (open sicilian/anti sicilian, panov/ classical). This would be a major decision factor.

I feel najdorf would give you a greater chance of winning, however it is much more difficult to handle (increasing your chance of losing). The caro is a bit more managable. This would factor in a few ways, 1.Is your opponent known for having good calculation ability? 2.How tired are you? have you played a few games that have been drawn out, or is it your first game of the day?.

another im sure will be mentioned is rating (I assume people will suggest playing najdorf against lower opposition and caro against higher).
Though im not sure I agree with this, both are quite capable of giving you solid positions with winning chances.

Which opening system you choose (Sicilian Najdorf or Caro-Kann in this case) in a particular game is arguably a function of a few different variables, including (though not necessarily limited to):
1.) which system you know better/feel more comfortable with (even if you know both reasonably well, you undoubtedly know one better than the other)
2.) whether or not (as user Assault has already mentioned) you know ahead of time that your opponent is less prepared for one opening system or the other (which you can reasonably ascertain if you have access to enough of his previous game scores).
3.) your opponent's rating. There are various theories on how you should tailor your opening repertoire based on this factor. Mine is that lesser rated players (i.e. those you should statistically win against more often than not) you should feel free to try out less familiar lines against, while the stuff you know best should be kept for stronger opposition.

Me personally, I would choose a Caro-Kann over a Sicilian any day, though I admit that I'm biased against Sicilian's these days. The Sicilian's an extremely rich defense that has lines that should suit any player's fancy. Unfortunately, there's also tons of theory to study (particularly in any of the Open lines), so for that reason, I long ago decided to stick to slightly simpler opening choices.

When talking about someone like Anand he would consider things like the opening specialty, strengths, and maybe even age of his opponent.  Najdorf has a lot of theory, so young opponents may be bad... but Najdorf can also have very sharp positions and young players can have an edge in calculation.

Depending on the caro line it may be very slow and strategic frustrating a wild player.  Maybe his opponent is known to play certain lines and Anand has some home preparation to spring a novelty.  Maybe his opponent is an opening specialist in one of them... things like this.

This is what I do. Let's say that I'm playing in a state championship tournament. I have won my first two rounds. I am a 2-0 on the standings. In the 3rd round I am paired with the highest rated player in my section. I have the Black pieces. I would choose to play the Caro-Kann for the following reasons:

1. I consider the Caro-Kann a drawing weapon.

2. If I can nick a higher rated opponent for a 1/2 point that is a win in my book.

3. With 2 1/2 points going into the 4th round, I stay with the leaders 1/2 a point behind anybody at 3-0.

4. I stay in contention for the money.

Thanks for all the helpful responses!

good question and discussion.

oh so true. especially whether or not you have specific knowledge of what your opponent will play. 

I think it is good to have 2 openings against e4, one safe and one more risky

play the najdorf against a weaker opponent to reduce his drawing chances and play the caro-kann against a stronger opponent to draw

At your or my level (looking at your blitz rating), the Caro-Khan is no more drawish than the Najdorf. But it's much more positionnal. Try to put your opponent in a position he don't like to play.

I think another thing to consider is that at the lower levels, players might not know or might not want to play the Open Sicilian.  So, instead of being able to play the Sicilian Najdorf, I might instead be stuck with an anti-Sicilian that requires a different strategy (not that that's a bad thing, as many anti-Sicilians stink.  ;) )

With the Caro-Kann, I reach that opening after 1 e4 c6.  Might not reach the main line, but the general idea of playing ...d5 remains.

And what if your opponent chooses to play something else at his second move, like the Morra gambit or the Grand-Prix Attack? Or if he decides to avoid the theoritical lines and to play the Alapin? Or if he plays 2.Nf3 and then 3.c3 (delayed Alapin).

The Caro-Kann, although more drawish than the Sicilian, doesn't put you in such complications, because as gundamv said, the idea of 2...d5 remains there.

However, most of the anti-sicilians aren't that fantastic (well except if black falls in a trap!) and get drawish if black plays accurately.

I'd say you to stick to your favourite one, no matter which one it is.

I totally agree with rolex575. Regardless of which defence it may be, (Sicilian Najdorf or Caro-Kann), as long as you have a good (and very deep) understanding of the mentioned defences inside and out, you'll do just fine. 

Whether the defence is drawish or not, should you be more concerned on the endgame? But again, it really depends on how you play them

Saying that one is better than the other is a bunch of horsesh*t.

What it boils down to is these 3 questions:

1) Are you in desparate need of a win?

2) Can you tolerate a draw?

3) Would a loss kill all hopes?

If the answer to #1 is yes, then play the Najdorf.  An example of this is you are in a 5-round tournament, it's now round 4, and you have 1.5/3.  If you want to win any money at all, typically 3.5 out of 5 seems to be the threshold in most 5-rounders I've been to.  Also, many final round scenarios are a must-win scenario.

If the answer to #2 is yes, then the Caro-Kann is safer.  It has a higher draw ratio than the Najdorf (not ungodly so like the Exchange French), but also, it leads to fewer losses.  A prime example of this is you go into round 3 with a score of 2 and 0 and you have Black.  The Caro-Kann may be the way to go.  If you draw, so what, you are still in really good shape.  You don't want the dreaded loss.

If the answer to #3 is yes, then by all means play the Caro-Kann.  A prime example of this is you have 2 out of 3 going into round 4 of a 5-rounder.  You have Black.  If you target that 3.5 threshold, a draw doesn't kill you.  A win would be great, but a loss kills all hopes.  Odds are you will get White the final round.  Play for the win then.  If you win round 4, great, but a draw is a thousand times better than a loss in this scenario, so the Caro-Kann is the better move.

If the answer to #3 is no, like in round 1, where a loss isn't the end of everything (you could win the last 4, or some let you re-enter), then take your chances and play the Najdorf if you got stuck with Black.

So it boils down to being "situational".

Flip a coin. 

Excellent analysis.

Thanks for the advice.

that's good tournament strategy. it also depends on the level of the opponents, you may want to draw against a stronger opponent and to win against a weaker. another example :  it's round 4, you have 2/3 and you're playing against a slightly weaker opponent with black. if you win this round, you'll probably face a stronger opponent in round 5, lose and finish with only 3/5. to increase your chances, play the caro-kann and offer a draw, then try to win round 5 with white against another slightly weaker opponent, and finish with 3,5/5.