What is the best opening for black


Suppose that you and your buddy were both being chased by a bear.
In order to get away safely, you don't need to be able to run faster than the bear.
You just need to be able to run faster than your buddy.
Similarly:
You do NOT need to study the Sicilian in-depth in order to play it against players of your own playing strength. You do NOT need to know all the lines and traps well enough to hold off a Grandmaster. You won't be facing a Grandmaster. You'll probably be facing someone who knows even less about the Sicilian than YOU do... because he was warned not to bother looking into it.

Suppose that you and your buddy were both being chased by a bear.
In order to get away safely, you don't need to be able to run faster than the bear.
You just need to be able to run faster than your buddy.
Similarly:
You do NOT need to study the Sicilian in-depth in order to play it against players of your own playing strength. You do NOT need to know all the lines and traps well enough to hold off a Grandmaster. You won't be facing a Grandmaster. You'll probably be facing someone who knows even less about the Sicilian than YOU do... because he was warned not to bother looking into it.
Even though we might not need to know every variation, we should be careful to claim that we know everything if you really dont. Because this was what the original post claimed that I responded to.

In response to all the people recommending the Caro, the Short variation is a very strong counter to it.

It's an issue for me right now. I never studied openings, didn't even know what mine might be called until a few weeks ago.
As White, no problem: it's what I was playing already, it's simple and easy to remember... the London, except I put the Knight on c3, so the Jobava London. Finding out its name was helpful... thanks to Lichess's Interactive Lessons feature, also to YouTube, especially Igor Smirnov and Ben Finegold... and players here.
As Black, I've struggled. I looked at a lot of openings and went with two Gambits, the Rousseau against e4 and the Budapest against d4. The Rousseau is complicated, but I like it... at first, it looks like you don't know how to play. The Budapest, same thing, though less so.... my take anyway. I still like them, but my opponents are not cooperating... I've considered giving them hints so they'll stay in book longer ("Nc3, bro, Nc3!").
So I'm moving on... against e4, I'm going with the French, on the advice of @MaetsNori. Against d4, I'm not sure.

As Black, I've struggled. I looked at a lot of openings and went with two Gambits, the Rousseau against e4 and the Budapest against d4...
I used to play gambits (Christ, I used to play the Muzio, sacrificing a Knight on move 5) but as my rating increased and I faced tougher opposition, I started finding it very limiting since my opponents would know exactly what sort of position I was aiming for, and act pre-emptively to avoid it.
So instead of playing gambits where I sacrifice material in return for development, I switched to playing lines that involve a positional "sacrifice" instead... saddling myself with a backward Pawn, or delayed development, or allowing the opponent a broad Pawn center.
I found that openings like the Sicilian Najdorf and the King's Indian (or the Benoni) Defense had very much the same unbalancing effect as my earlier use of gambits, but were much more difficult for my opponents to avoid unbalancing lines.
The French would also be a good choice. Strategically speaking, the French is a very ambitious opening. People who call the French "passive" have no idea what they're talking about. Black's very first move (1. ... e6) prepares to strike at White's proud e4 center Pawn with 2. ... d5. Black is attempting to dictate both the place and the time of the battle... a very ambitious idea.
But against 1. d4 I would suggest either the King's Indian or the Benoni. KID is especially recommended as it is strong against the London, a popular system for White.

Okay then. Thanks!
and very interesting, this:
"Strategically speaking, the French is a very ambitious opening. People who call the French "passive" have no idea what they're talking about. Black's very first move (1. ... e6) prepares to strike at White's proud e4 center Pawn with 2. ... d5. Black is attempting to dictate both the place and the time of the battle... a very ambitious idea."
I actually have a Lichess study open in another tab right at the moment, the first I've ever given the French any thought.
I guess I might need to reconsider the King's Indian.
But... "Benoni", I'm looking at that first.

Playing the King's Indian Defense as Black just requires wrapping your head around several of the typical ways that Black generates PLAY in the King's Indian.
You don't need to fear White's broad Pawn center. Every Pawn move leaves weaknesses in its wake. As the position opens up, those weaknesses become more acute. Black just needs to ensure that as the position opens up, his own piece activity increases in proportion.
Here's a rated game from a club vs club match.
You will know every variation of the opening and all the traps
There is no such things as knowing all variations and all traps in the sicilian. Grandmasters who have studied a specific sicilian come close to this. But one person will not be able to solve the sicilian alone.