I’d recommend looking up each line, reading the Wikipedia article on it and seeing some games in each line, then see what you like/find interesting and go with it
All the lines are sound and vary in tactical and positional elements (And some are very different from each other...)
There is no one-size-fits-all solution: it depends on your strengths, weaknesses, time you want to spend on memorizing theory, etc.
The only thing I would add to post 2 is "Not the pin variation". That us one of those lines where you catch a low rated player off guard, but against anybody that knows what they are doing, Black gets a very miserable position in that line.
The rest? Again, see post 2.
I just find if I'm playing as white, I have ideas against most systems but less so against the Classical. Plus, I got some inspiration from the candidates tournament final round Richter-Rauzer between Karjakin and Caruana (Ironically, white won that critical game and Karjakin went on to face Carlsen).
Open Sicilians are a vast territory. Mastering even a single area, like the Scheveningen/Najdorf complex, is daunting.
As Black I try to avoid the open Sicilians by starting with the Old Sicilian move order, viz. 1 e4 c5 2 ...Nc6 . Moving 2 ...d6 allows the enormous possibilities of the open Sicilians. In local clubs & tournaments my opponent will respond with an anti-Sicilian about 75 - 80 % of the time.
There are only four major anti-Sicilians : Alapin , Rossolimo, Smith-Morra and the Grand Prix Attack. Preparing for only these drastically reduces my study. If my opponent pursues an open Sicilian I just try the best I can with a Sveshnikov or possibly a Scheveningen with Najdorf move order.
Four knights is the easiest, and the less theory-heavy.
I agree with pfren. Nobody plays the main line with Ndb5 on amateur level.
The only guy that played Ndb5 against me was an International Master hand he absolutely obliterated me.
You will never encounter the critical lines at amateur level. If you play the najdorf however you can sure that you will run into a lot of concrete or complicated lines. The four knights is prettt straight forward.
Knights to f6 and c6, bishop to b4 and d5 if possible.
With that knowledge you can already play some blitz or tournament games. You almost have nothing to prepare.
Later you can look at some gm games but apart from that you can be sure that there won't be any surprises in the opening.
Dragon systems probably easiest to get a good grasp of especially when there are so many g6 systems against a lot of the sicilian sidelines. But I think whatever system you might choose the reward from studying the depth involved in all of them is a good thing.
Four knights is the easiest, and the less theory-heavy.
I agree with pfren. Nobody plays the main line with Ndb5 on amateur level.
The only guy that played Ndb5 against me was an International Master hand he absolutely obliterated me.
You will never encounter the critical lines at amateur level. If you play the najdorf however you can sure that you will run into a lot of concrete or complicated lines. The four knights is prettt straight forward.
Knights to f6 and c6, bishop to b4 and d5 if possible.
With that knowledge you can already play some blitz or tournament games. You almost have nothing to prepare.
Later you can look at some gm games but apart from that you can be sure that there won't be any surprises in the opening.
I have to admit that does look easy to play. Also looks similar to a good version of a french. I probably really could just start playing that immediately while Im learning the dragon.
Four knights is the easiest, and the less theory-heavy.
I agree with pfren. Nobody plays the main line with Ndb5 on amateur level.
The only guy that played Ndb5 against me was an International Master hand he absolutely obliterated me.
You will never encounter the critical lines at amateur level. If you play the najdorf however you can sure that you will run into a lot of concrete or complicated lines. The four knights is prettt straight forward.
Knights to f6 and c6, bishop to b4 and d5 if possible.
With that knowledge you can already play some blitz or tournament games. You almost have nothing to prepare.
Later you can look at some gm games but apart from that you can be sure that there won't be any surprises in the opening.
I have to admit that does look easy to play. Also looks similar to a good version of a french. I probably really could just start playing that immediately while Im learning the dragon.
I forgot to mention that the reason why it is very unlikely that they enter the critical lines is that these variations require them to know concrete lines from which they can't deviate unless they want to have a disadvantage.
Also the main lines require them to move their pieces twice or more times. These critical moves are the best but require them to make unnatural moves over the board which isn't actually going to happen over the board when they don't know the precise moves.
IM Eric Rosen actually recommends this opening for many of his students, because it's a good and practical opening with not much theory to learn. Black plays simple and active moves while white has to find unnatural moves over the board. If you play an opponent whonjust plays natural looking moves you basically equalize immediately.
The rest is up to you to win this position. Once you equalize that early in the ooening you can play for more.
As mentioned above you can look up in a database for GM games in the main line. I recommend Kramniks games.
The good thing is, that once you studied it you can play it for live and have decent results because if your opponents deviate from main line theory which will happen in a lot of cases, you equalize immediately with Bb4 and d5 in most cases. The amount of theory and preparation is laughable compared to the najdorf. You still have to put some work into it but it's not much.
There also some youtube videos which are enough to get youbstarted. Just play the opening and learn through experience. You don't have to now everything right now. Just play it and analyze your games extensively afterwards.
Here is also an interesting discussion, where also IM pfren gave his input about the four knights.
https://www.chess.com/forum/view/chess-openings/the-sicilian-four-knights-a-good-practical-opening
The one downside to the four knights or any 2...e6 Sicilian (I played the Taimanov for about 2 years) is a large increase in 2 Anti-Sicilians. 3.b3 (many be players only do so when ...e6 is committed and will play something else, like 3.Bb5 against 2...Nc6 or 2...d6) and 3.d3 (Kings Indian Attack).
I found 3.b3 a tad bit annoying over the board but was no problem at all in correspondence. 3.d3 I would transpose to KIA vs French.
What made me quit the Sicilian is the open Sicilian, but for some others, certain anti-sicilians do them in.
Usually, if you are a Sicilian player, you are going to know how to defend the generic anti-Sicilians, like the closed or grand Prix or Alapin. It is usually the ones unique to your second move that seem to do most people in (or else the Open Sicilian, like in my case).
The ones you have to watch out for are:
2...d6 players - Deferred Alapin - 3.c3 - unlike against other 2nd move responses, this does not transpose. It is a whole different ball of wax.
2...Nc6 players - Rossolimo
2...e6 players - 3.b3 and KIA.
The one downside to the four knights or any 2...e6 Sicilian (I played the Taimanov for about 2 years) is a large increase in 2 Anti-Sicilians. 3.b3 (many be players only do so when ...e6 is committed and will play something else, like 3.Bb5 against 2...Nc6 or 2...d6) and 3.d3 (Kings Indian Attack).
I found 3.b3 a tad bit annoying over the board but was no problem at all in correspondence. 3.d3 I would transpose to KIA vs French.
What made me quit the Sicilian is the open Sicilian, but for some others, certain anti-sicilians do them in.
Usually, if you are a Sicilian player, you are going to know how to defend the generic anti-Sicilians, like the closed or grand Prix or Alapin. It is usually the ones unique to your second move that seem to do most people in (or else the Open Sicilian, like in my case).
The ones you have to watch out for are:
2...d6 players - Deferred Alapin - 3.c3 - unlike against other 2nd move responses, this does not transpose. It is a whole different ball of wax.
2...Nc6 players - Rossolimo
2...e6 players - 3.b3 and KIA.
b3 doesn't happen that often. I'm very glad if my opponent doesn't play main lines. I prefer this over thoretical positions. Against b3 I like d5. Aronian played like this and I like the resulting positions.
Against the KIA I like the approach where black develops with Nc6, Bd6, Nge7, Dc7 and if e5 is a threat f6. White never manages to play e5 in these positions. I never had a problem against anti-sicilians, because they always get fresh positions on the board with chances for both sides.
I play b3 myself because there is an overlap with my repertoire against the french.
Hi 
I have an elaborated notation of Sicilian Defense (Paulsen System). If you are interested in it, you can write me a private message, I can teach it to you. I am an official coach, so I can improve all of your skills in openings, middlegames and endgames, too. I charge 30 USD or 25 EUR per hour. I am looking forward to your message.
Gabor
Yes... paulsen kan type hedgehog is a good sicilian intro... and acceptable at GM level. But even these have lots of lines and can be confusing. But studying can be fun?
Sure, it can be fun, becuase there are unusual lines, which I play and can be dangerous. I really like it and won a tons of games in that. If anyone is interested, can write me a message and we can discuss the details. 🙂
I played b3 lines against e6 Sicilians for a while, but gave them up because I realized I didn't know what I was doing. Where do you put the light-squared bishop? If it comes out to c4, it gets harried by Black's queenside pawns, while developing on g2 or e2 look a bit slow.
But that's the sicilian bro? Such complex tactics are why strong players luv... pet lines like smith morra and alapin are not feared by serious players. Strongest bet... open variation. If you have a few yrs to study...
Najdorf? Dragon? Classical? Scheveningen? Sveshnikov? Accelerated Dragon? Kalashnikov? Taimanov? Kan? Four Knights? Pin Variation?
There have already been some good answers, but another way to answer this question for any opening choice is this: What player do you enjoy studying?
If you enjoy studying the games (specifically the Black games vs 1. e4) of Fischer, Kasparov, or MVL, the Najdorf would be your better choice as you will see a LOT of those games at a very high level.
If you enjoy the games of a young Nakamura, or Gawain Jones, you will likely want to look at the Dragon.
If you enjoy studying the games of Magnus, the Sveshnikov.
If you enjoy studying Harikrishna or recent Shankland games, you will likely want to look at the Taimainov.
If you like facing the Maroczy Bind, play the Accelerated Dragon.
I would avoid the Pin Variation as Black's position is just bad if White knows what he is doing.
You can use the same process for any opening choice down the road.
Najdorf? Dragon? Classical? Scheveningen? Sveshnikov? Accelerated Dragon? Kalashnikov? Taimanov? Kan? Four Knights? Pin Variation?