Best opening with black

The March 2019 issue of Chess lists the top twenty openings compiled from a list of 2458 January games where both players were rated over 2400 Elo. One can not take position on this list too seriously because it is greatly influenced by how the openings are grouped. For example, all the Retis are grouped together, while English is separated into 1...c5, 1...e5, etc. Nevertheless, for what it is worth, some of the list entries are: 180 Retis, 129 Caro-Kanns, 102 King's Indians, 84 Nimzo-Indians, 80 declined Queen's Gambits, 74 Najdorf Sicilians, 69 Slavs, 60 1...e5 Englishes, 58 1...Nf6 Englishes, 53 Berlin Ruy Lopezes, 51 1...c5 Englishes, 50 Kan Sicilians, 50 Giuoco Pianos, 49 Classical Gruenfelds, 46 3 Nxe5 Petroffs, and 44 Taimanov Sicilians.

"... A typical way of choosing an opening repertoire is to copy the openings used by a player one admires. ... However, what is good at world-championship level is not always the best choice at lower levels of play, and it is often a good idea to choose a 'model' who is nearer your own playing strength. ..." - FM Steve Giddins (2008)

The "best opening" is the one that leads to a position in which you feel comfortable and confident. At our level of play, the opening serves no other purpose.

1...c5, 1...c6, 1...e5, and 1...e6 are the four soundest responses to 1.e4.  Other moves, while playable, are weaker.

Which of those 4 is best?  As others have already mentioned, whichever best fits you!  For me it's 1...e6 and 1...e5.  For someone else, it's 1...c5.  For someone else, it's 1...c6.

Don't bother asking which of the four is best.  You got as clear of an answer you will ever get!

I have good luck with E5

You have to build your own opening library and stay with it, on e4 I'm playing the French defence.

This is misleading. It's true that the Sicilian is a good response to 1.e4, but it's not the best - it's just one of several reasonable responses.

Best:

1...e5 - Open Game

1...c5 - Sicilian

1...e6 - French

1...c6 - Caro-Kann

Perfectly reasonable:

1...g6 or 1...d6 - Modern Defense

1...d6 - Pirc

1...d5 - Scandinavian (I think some people would put this in the 'inferior' section)

Slightly inferior or bad:

1...d6 - Philidor

1...b6 - Owen's Defense

1...a6 - St George Defense

See these are not all equal, but the first four certainly are - it's not true that the Sicilian is better than the French for example. Also, 1...d6 can be several things depending on how you follow it up, a Pirc is not guaranteed.

What about 1...d5, 1...Nf6, and 1...Nc6 ?

By the way, about eight years ago, IM Greet wrote a book to help 1 e4 players with the alternatives to 1...e5, 1...c5, 1...c6, and 1...e6. According to one review, the topics of Beating Unusual Chess Defences 1 e4 were: Scandinavian Defence, Modern Defence, Pirc Defence, Philidor and Czech Pirc, Alekhine’s Defence, and Other Defences.

http://marshtowers.blogspot.com/2011/11/chess-reviews-190.html

"... If you play 1 e4, then you have to be ready for a wide array of defences. The Sicilian, Caro-Kann, French, and 1...e5 are all huge topics, ... But ... there are numerous other less common but still highly respectable defences for which one must be prepared. The Alekhine, Modern, Pirc, Scandinavian, and others all require serious attention, ... I have laid out a comprehensive repertoire for White against each of the aforementioned openings, plus all other irregular defences after 1 e4 which fall outside of the 'big four'. ..."

https://www.amazon.com/Beating-Unusual-Chess-Defences-Scandinavian/dp/1857446216

I didn't include these because the person I was responding to didn't either

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OK, me being careless

My personal favorite is the French opening against e4 (Line: e4 e6 – d4 d5 – e5 c5). More often than not, opponent blunders in the opening phase against French at my level (around 1300). Other openings that I like are:

• Sicilian Defense: e4 c5 – Nf3 d6 – d4 cxd4
• Scotch Game: e4 e5 – Nf3 Nc6 – d4 exd4

there's no way the Philidor is in the same category as a6 and b6 (yes I know it was years ago but still)

The engine prefers 1. c5, but truly, the best opening could be anything that you win consistently with, whether it be the Sicilian or the Scandinavian or the Caro-Kann or even the St. George. Play to your strengths (and your opponent's weaknesses) and you'll do well no matter what your engine says is best.