Caro Kann versus 1.e4, QGD with a6 versus d4 and so ..., d5 versus Nf3, etc.
For me, one answer to each has long made sense. This gives a chance to play enough of any one line to get a feel and truly understand the theory.
I will continue to do this, certainly for the QGD as I don't face d4 / c4 enough. I would like to add the Sicilian Kan though.

Marc Benford wrote on 01/11/24 at 18:53:15:

Well I think the Modern Defense 1..g6 counts as only one. Even if 1.d4 g6 2.c4 Bg7 3.e4 d6 4.Nc3 black can stay in independent waters. Maybe you could argue 1.b3!? avoids it. Also there is a universal 1...d6 2...c6 (or vice versa) "busy-person special" analysed by Davies (and by Wincor before him).

At one time I played "everything". In other words I didn't have any deep opening prep anywhere, rather I played hit-and-run against each opponent. Then when I needed to face titled players I went to the other extreme and played a very narrow 1.e4 e5 and 1.d4 d5 repertoire. Better openings and better chess overall, but it was a bit of work since my opponents could count on me to play the same opening when we met again. Also I had to accept an unwanted draw from time to time. These days the trend with titled players is to play varied openings, to avoid falling into some memorized computer line. Preparing one super-sharp line is possible, preparing three is too much of a strain, and even preparing one such line is discouraged if there's only a 33% chance of using it. That makes sense to me, so I have added a couple of alternative defenses against each of 1.e4 and 1.d4.

There is no option for 1 because you can't play only 1 defense. You must have at least 2 defenses: one against 1.e4 and one against 1.d4/Nf3/c4.

Defenses which you know and which you played in the past but which you don't play anymore do not count as part of your repertoire.

How wide or how narrow is your repertoire?

How wide or how narrow should a repertoire ideally be?

Within the same one defense, do you always play the same one variation or do you vary by playing multiple variations?

As Black I play only two defenses: the Double King's Pawn and the QGD. But my repertoire is actually wide, because I don't always play the same variation, I vary.
- In the QGD, I play the Tartakower, the Lasker, the Vienna, the Tarrasch, the ...a6.
- I play the Closed Spanish 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 d6 8.c3 O-O 9.h3, but then I play all the possible 9th moves.

As White I play 1.e4.
- Against the French, I play the Advance and the Exchange.
- Against the Double King's Pawn, I play the Spanish, the Italian, the Scotch, the Four Knights.
- Against the Caro-Kann, I play 3.Nc3 6.Nf3, then I play 7.Bd3 and 7.h4 h6 8.h5 Bh7 9.Bd3.
- I play the Open Sicilian, 6.Be3 and 6.Be2.