what openings to play when?

I have tried to ask this question once before, but without much success. Anyway I will try again. 

In any sport you can only meet three types of players. A player that is better than you, a player that is equal, and a player that is weaker than you. This in turn tell me that I need only to play 6 openings. 3 for white and 3 for black. 

What 3 openings do you think I should play against a weaker, an equal and a stronger player as black, and the same for white?

Wrong approach!

It's not about weak and strong.  It's about style.  If you research all of your opponents, you might have an opening to play against aggressive, impatient players and another for those that prefer safety and a slow and methodical approach.

In other words, you see who you are facing in say, the 4th round the US Open, and you do your homework, and you see that he's a very aggressive, tactical play that plays nothing but the Najdorf, Grunfeld, and very aggressive variations of e4 openings.  You know you are going to get Black against him.  1...e5 or 1...c6 is probably your best bet.

Next, in round 5, where you know you are getting White against a very cautious player that plays the Sicilian Kan.  Maybe throw the Morra Gambit against him, and if he goes c3-Sicilian on you, there are options for White to push.

It's not about weak and strong.

I think many players adjust their play in reaction to the playing strength of their opponent, but I would guess that it would be too much work to try to have 3 different white openings, 3 different reactions to 1 e4, 3 different reactions to 1 d4, and so on. Even just for White, it is more complicated than you might think. The Ruy Lopez is a plausible choice, but it is not possible for White to decide that the game will be a Ruy Lopez without Black cooperation. White can play 1 e4 with the HOPE of getting a Ruy Lopez, but the player might be compelled to deal with, for example, 1 e4 c5. In any event, nobody can realistically choose openings for you. "You find your own path by walking it." Only you can decide whether or not you are comfortable with this or that opening. Some experimentation is necessary. If you really want suggestions, you can go to Openings for Amateurs by Pete Tamburro (2014).

http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html

I believe that it is possible to see a fair portion of the beginning of Tamburro's book by going to the Mongoose Press site. Perhaps you would also want to look at Discovering Chess Openings by GM Johm Emms (2006).

https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf

Thriller fan. I totaly agree, that is why I limit this to online chess, where you dont know your opponent before the game starts. 

Ylblai2, I see your point. Still, if you want to get better, you have to start somewhere right?

So lets limmit ourselves to white, that would elliminate half of the options 

With white you could play 1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. c3 Nf6 and now the solid 5. d3 or the more active and risky 5. d4 or the evans gambit with 4. b4. Or after 3... Nf6 the quiet 4. d3, the active 4. d4 or the pawn grabbing 4. Ng5.

The idea is that you first have one line nearly everywhere before you add a second line against some openings. E. g. After 1. e4 e5 2. Nf3 you should have lines against the two knights, the petroff, philidor, latvian and elephant gambit before adding a second line against 2...Nc6 3. Bc4 Bc5.

If you play 1. e4 or 1. d4 with white you have to learn too many lines.

With black you could have the choice between a solid and a more counter attacking option, e.g. after 1. e4 e5

italian game vs. two knights

closed ruy lopez vs. marshall or schliemann

or after 1. d4 d5 2. c4

slav or qgd vs. albins counter gambit or some tarrasch lines

But at my low playing strength i think one should concentrate on one line everywhere. It's not practical to learn more!

Play the board, not the rating.  

In some cases you might want to have more than one repertoire, but in most cases I don't think it's needed for non-masters.

I play the English, the Caro-Kann, and the Slav regardless of whether my opponent is weak or strong. Some people might think this approach is bad against lower rated opponents, especially the Slav because of the Exchange variation, but so far I've found that it's rather easy to mix the game up and create winning changes.

(This is what I play, not what you should play)

As white, I always play 1.e4

As black, I see what white does.

If he plays 1.e4, I like to play 1…d5 (Scandinavian defense).

If my opponent plays 1.d4, I always play 1…Nf6 (Indian game), hoping to transpose into a Nimzo-Indian (2.c4 e6 3.Nc3 Bb5) because I have 100% win rate with it “lmao”

It depends on how you can veer him into either your repertoire or unfamiliar territory for him 

e.g. 1.d4 c6 2.e4 Nf6! Caro-Kann Defence: Masi Variation

1.d4 c6 2.e4 f5 Caro-Kann Defence : Massachusetts Defence 

1.e4 e5 2.Nf3 Nc6 3.Bb5 Qf6! Ruy Lopez : Gunderam Variation

1.e4 a6! St George Defence 

1.c4 b5 English Opening : Jaenisch Gambit

e.g. 1.d4 e6 2.e4 Nf6! French Defence : Mediterannean Defence