I am an amateur player and do not have much time to study and memorise complicated opening lines. Am wondering after 1.e4 e5 2.Nf3, if 2...Nf6 is a safer and simpler option for black than 2...Nc6. My database shows that after 1.e4 e5 2.Nf3, the move which gives white the lowest winning percentage is 2...Nf6 instead of 2...Nc6.
As an amateur player, you should know the connotation that 2...Nf6 (The Petrov defense) has a reputation of being more boring and more of a draw than 2...Nc6 (leading to the Ruy Lopez, Italian, and Scotch games). However, this really doesn't apply at the amateur level. In fact, you're much more likely to win or lose than draw, unlikely to the masters' database showing that certain lines have a drawish tendency.
So my suggestion, as unexciting as it is, is play what you like! Try out Nf6, try out Nc6, and see what pawn structures/middlegames you're getting in your games. Do you like them? Do you prefer one or the other? Play that one more often!
Objectively speaking, 2...Nc6 is the strongest reply. That's why it's preferred by most top players. 2...Nf6 is an interesting alternative, but it often leads to more drawish positions after 3.Nxe5 d6 4.Nf3 Nxe4, but White can also go for 4.Nxf7!?, which is an inferior line, but very sharp and it can put you in big trouble if you don't know it well.
So it all boils down to what you feel more comfortable with. Both moves are perfectly playable but you need to figure out what type of position you understand better.
If you want to play 2...Nf6, you'll have to be ready for the 4.Nxf7 line, and also understand how to play in those positions with the open "e" file. White can also try 3.Nc3, with a transposition to the four knights opening after 3...Nc6, which is its own story but still not as hard to learn as 2.Nc6 as White has lost a lot of its flexitiblity (most lines in the Italian or Spanish openings play a c2-c3 push at some point.
On the other hand 2...Nc6 will need you to be ready for (mainly) 3.Bb5, 3.Bc4 and **3.d4, all of them being very complex openings with a lot of theory on them.
Finally, even if your skill level doesn't directly play a role on which one to choose, it will definitely have an impact on the time that is worth dedicating to openings. If you're not a particularly strong player, you may want to play 2..Nf6 just to need less studying and move on to things like tactics and strategy, but in that case you may also want to play a completely different defense.
The Petrov is a sound opening but the problem is that white can basically force a queen trade in a symmetrical position. For example- 1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4 5. Qe2 Qe7 6. d3
That's okay for a GM but bad for a developing player for two reasons:
You aren't going to get better playing these types of positions. There aren't a lot of tactics and the endgames are going to be boring attempts to draw rather than learning how to win.
If the Petrov is your only defense to e4 that means you're going to have a lot of situations where you're playing someone rated 500 points below you and you can't find a way to win because they're just trading pieces.
A good starter opening is the Scandinavian. If you know the line 1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 and understand a few general ideas you can get a playable game against anyone.
When you get a little better and want to expand your rep then look at 2...Nc6. The Ruy Lopez is really all you have to worry about. You can equalize against the other lines fairly easily. Against the Ruy you have a lot of choices. If you don't play 3...a6 you cut out 90% of the theory. My favorite is the classical (3...Bc5). Black has an active and solid position but without a lot of theory. There's other options too like 3...d6, 3...Nge7, 3...Nd4 etc. 3...g6 is rarely played but probably fine. There's other options to avoid theory even after 3...a6. Just find a line you like that gives you reasonable chances. You won't see it that often anyway until you start getting pretty good.
After you get around 18-1900 you can look at other openings and start narrowing your rep. Below that point, theory isn't all that important. Most games don't go more than 4 or 5 moves deep into theory and you're just looking to get a playable position against the guy who memorized a single line 30 moves deep or the guy who learned a couple of traps. What you learn from the types of positions you get is the most important thing. The openings that will make you better are the ones that give you sound, active positions while avoiding theory and drawish positions.
For practical reasons, 2...Nf6 is better for you than 2...Nc6, because 2...Nc6 does not make a threat, and your opponent won't have to think about anything. But if you counterattack with 2...Nf6, then your opponent has to think, and that's what you want: your opponents thinking for themselves.
That's in practice. In theory, 2...Nf6 can be safer than 2...Nc6, can also be wilder. Depends on where the players take it, in practice. Your opponent has 50 percent of the say about whether your moves are safe.
Is it easier to learn? What does that even mean?
If you think "learning an opening" will help your results, that's nonsense. The best chess teacher ever, Cecil Purdy, said: "Some players think they could play a good game 'if they only knew the opening'. This is just crazy."
Why do you think you need to learn an opening? This is the dumb idea that 99% of chessplayers have. Your only real job in the opening is to reach a playable middlegame, one with rough equality in center control, development, and king safety. You can get there playing whatever you want, as long as you're mindful of the general principles of the opening, and especially of the tactics. Chessplayers are pretty dumb about this: They think they lose in the opening because they're bad at the opening. They lose in the opening because they're bad at tactics.
Let's say you want to be dumb about it, like your friends and neighbors, and you think you absolutely must know something about 1. e4 e5 2. Nf3 Nf6 to survive your next session of play. Here's what they will tell you here on StackExchange: It's more important to know the ideas behind an opening than memorizing the moves in that opening. That is actually code for: Give me fewer things to remember.
Chessplayers sort of figure out through experience that memorizing strings of moves gets them nowhere. Their opponent will vary from their book knowledge, then they are floundering. Or they reach the end of their book knowledge with a magical +=, but then what? Then they're wandering around lost in the middlegame. So chessplayers say "if you learn the ideas, you can find moves based on the ideas". And because there are fewer ideas to learn than strings of moves, chessplayers think they've got opening learning figured out. This doesn't drill down deep enough. What if — instead of knowing the ideas behind one opening — you knew the ideas behind all the openings? This will save you untold hours of study time, understanding that if you're playing to maintain at least one pawn in the center, maintain roughly equal development, and tuck your king as safely as his, you'll be OK.
I already said that people who "learn" openings get lost in the middlegame, rendering their opening knowledge moot. It helps your opening play if you know what your rooks are doing during the middlegame. Purdy said: "The real test of one's opening is the play it gives the rooks." Primarily because of what grandmaster Fine said about favorable middlegames: If you have emerged from the opening with better center control, better development, and better king safety, you clearly have a superior middlegame position. And from a superior middlegame position, attack the enemy king by opening files for your rooks.
But sometimes you can't checkmate them, and it's impossible to avoid an endgame. The endgame is inevitable. You cannot put pieces back on the board to the second move and play 2...Nf6 all over again, you will reach endgames. So it is imperative that you know what a favorable endgame looks like and what an unfavorable endgame looks like. Otherwise you will never know during the middlegame whether you want to swap units to simplify the position or to preserve units on the board to keep things complicated.
In other words, you can get through the opening with pretty much anything. Purdy said it's impossible to play a perfect opening, but it's pretty easy to play a decent one. And no matter what happens in the middlegame, you have to judge whether or not you want to head toward that endgame that's on the horizon. So learn endgames. You have to. A mistake in the opening will not kill you. A mistake in the endgame turns a win into a draw, a draw into a loss. Mistakes at the end are far more costly than whether Stockfish says one move in the opening is .35 better than some other move in the opening.
The beauty of this is that endgame can be learned, while the opening cannot. You can learn how to play perfectly every position with three units on the board. Then you add a unit, and learn how to play all the positions with four units on the board. Perfectly doable. And work your way backward. It took me 50 years; I'm still working on positions with four units on the board. So isn't it logical and common sense that if learning positions with few units on the board is more valuable and more doable, then that's far more important than wondering what to do at move 2 with 32 units on the board?
This might be LOTS more than you wanted to know, but if you want to get good at this, you have to know it, the sooner, the better. And by telling you, I get to tell everyone else reading it.