… A move that does the above while also increasing the difference between easy of play (in your favor) is best in a strong sense.
(Difference between ease of play meaning it's easier for you to find good moves than your opponent.)
Doesn't that depend on who is doing the playing?
As someone who is artistically inclined, I've got a hunch that the 'best' move is also the most aesthetically pleasing or beautiful one. Whether of course beauty in a move is determined by being a winning one, or if beauty just happens to coincide with being a winning one is a difficult point.
I once saw someone argue that 2...exf4 was aesthetically the best move after 1 g4 e5 2 f4.
… A move that does the above while also increasing the difference between easy of play (in your favor) is best in a strong sense.
(Difference between ease of play meaning it's easier for you to find good moves than your opponent.)
Doesn't that depend on who is doing the playing?
Yeah.
Is that a problem? You only play 1 person at a time.
As someone who is artistically inclined, I've got a hunch that the 'best' move is also the most aesthetically pleasing or beautiful one. Whether of course beauty in a move is determined by being a winning one, or if beauty just happens to coincide with being a winning one is a difficult point.
Yeah, as humans we give more weight to stuff like that.
I know in my games I'll avoid playing common mates if there is a different one available. Or if either piece mates, I'll choose the one that's not as valuable. Or if the ending position leaves all the pieces on the same color of square, I'll do stuff like that.
… A move that does the above while also increasing the difference between easy of play (in your favor) is best in a strong sense.
(Difference between ease of play meaning it's easier for you to find good moves than your opponent.)
Doesn't that depend on who is doing the playing?
Yeah.
Is that a problem? You only play 1 person at a time.
I suppose it might be a problem if one is writing a book with a best-move assertion.
… A move that does the above while also increasing the difference between easy of play (in your favor) is best in a strong sense.
(Difference between ease of play meaning it's easier for you to find good moves than your opponent.)
Doesn't that depend on who is doing the playing?
Yeah.
Is that a problem? You only play 1 person at a time.
I suppose it might be a problem if one is writing a book with a best-move assertion.
Yeah, like DS is saying this is more a philosophical musing than something practical.
If there is a 'best' move in every position, then by extension there is a single 'best' game, that should always be played! I've often wondered what this game is, for e.g. a given engine at a given search depth and whatever other settings they have to fix. Presumably, if the engine were to play itself it would play the 'best' move for both sides in every position and the result would be the perfect game of chess.
It's a rather depressing thought though, to be honest! At least thinking of top level chess. Down at our level the 'best' move is a very theoretical concept in many positions and we aren't good enough to find it anyway.
If there is a 'best' move in every position, then by extension there is a single 'best' game, that should always be played! I've often wondered what this game is, for e.g. a given engine at a given search depth and whatever other settings they have to fix. Presumably, if the engine were to play itself it would play the 'best' move for both sides in every position and the result would be the perfect game of chess.
It's a rather depressing thought though, to be honest! At least thinking of top level chess. Down at our level the 'best' move is a very theoretical concept in many positions and we aren't good enough to find it anyway.
Whether it's a win or a draw with best play it's not hard to imagine how there would be more than 1 perfect game.
In many positions there are many moves that maintain the win (or draw if it's a draw).
I once saw an amateur argue that the perfect game was 1 d3 d6 1/2-1/2.
Well, I did start by saying 'If there is a 'best' move', meaning one move that scores higher than all others, by whatever metric is used. Of course it is true that once an engine evaluates a 0.00 position then any move that maintains this is considered equal. But more imaginative metrics could no doubt rank many of these moves, if you were assuming a human opponent who might make mistakes more in response to some moves than others, even if, with best play, all would lead to a draw.
Yeah but that's not so depressing, at least it isn't for me, because it would always depend on the metrics.
As for hardest for a human to beat that might produce as many different games as there are humans so that's more interesting than depressing 
In the old days playing on FICS I recall some engine having an anti human mode. It made bad moves but you needed to see a lot of crazy tactics to refute them.
I'd say:
A move that maintains the true evaluation is best in a weak sense.
A move that does the above while also increasing the difference between easy of play (in your favor) is best in a strong sense.
(Difference between ease of play meaning it's easier for you to find good moves than your opponent.)
Thats circular logic tho. The evaluation is determined as a result of the upcoming best moves.
I'd like to elaborate on my earlier point on 'artistry' in chess. I do wonder if one could play chess and win by simply playing the most 'elegant' move on each turn?
This may seem fanciful, but it is the direct implication of the idea, that many people hold, of chess being an art form.
I think modern engines like Alpha Zero have provided some evidence for this idea.
Indeed. Aside from your question being "partly" rhetorical, technically a "drawn" position occurs mostly late middle game or early transition into the end game, therefore "partly" (or "mostly" to me) ruling out the discussion about 'no opening leads to a forced win for white and black should always equalize' ("in all likelihood"). It doesn't quite jive with me. Many openings are comprised of moves, lines, variations worked, reworked from generations upon generations of player's games of objectively "best" moves. The fact that players (like you stated) often times play mediocre, sub-par moves or outright deviate from the "best" path because (IMO) of their personal preference, familiarity, or ignorance especially in the opening, begs other questions in a practical sense: what IS the "best" move in a position where white has a slight plus or black has a slight advantage? Or the position is balanced but could go either way? Or just plain inaccessible (unclear)? Posing those kinds of thoughts make your opinion of what the "best" move is (to draw, not to lose) more credible.
I'd say the key distinction between "drawn" on the one hand and "even" or "equal" on the other is that the former reflects an assessment based (usually) on calculation and the latter two an assessment based on intuition. But otherwise they refer to the same thing. If I thought one side in a position might be able to force a win but I just couldn’t calculate it out to the end would I rate the position as "="? Probably not. I'd probably rate the side I suspected of having a win as having an advantage. And if I was so confused I didn’t know what to think I’d probably says "∞".
Someone might says equal means “equal chances” not drawn, but I’d personally fault an annotator for subjectivity who would assess a position like that. It's essentially saying “equal” based on the human equation and likely sub-optimal play by one side resulting in equal practical chances. If we go down that road we’re going to get ridiculous pretty quick. We’re going to have to consider every evaluation based on practical considerations, like the strength of the players or time period in history. Eg: “oh the Steinitz Gambit is -/+ now at the top level but was = in Steinitz day and is +/= at the club level these days except on a Tuesday…”
Sometimes the best move is the worst move
Indeed. I appreciate the callout @Ahptoemiz. I have soo many thoughts I'd like to convey but I'm guessing it would go in different tangents and off into other subjects beyond your forum, so I'll simply reply to your last point: I totally agree; human subjectivity, engine analysis notwithstanding, is always the main arbitrator of what objectively is the "best" move. "Hindsight" and past research being our number one criteria, our ability to evaluate in real-time based off of one's personal experience, knowledge & current information being a close second. There were many times after a game, when analysing a critical position after a game (whether I win or lost) I "found" the best move from a game played 30yrs prior, in the notes to the game. Cool. Or in another instance, what I thought was a gamebreaker was actually played by Steinitz!
With a Rubik's cube, when trying to solve it for the first time (yes, this is my "big" analogy) it seems impossible: any which way you turn it to solve one side jumbles up the other sides; you match 4 sides leaves you in a bad position to finally solve the last two sides. Obviously, there was a book written long ago to solve it however it was mixed up. It involved looking for a certain pattern on each turn. The "best" move. If you didn't follow that path, you'd likely come up short. In conclusion, yeah we're still chasing the "best" move in a game, but in my opinion, they are a plethora of known positions (ie the two bishop sac, rook exchange sac on Nc3, the infamous Bxh6 etc) that guides us often times to it. Nuances in the pawn structure, playing against an isolated pawn, overloading a certain point, weaknesses in color complexes, prophylaxis blah blah are all there. We just have to develop the ability to recognize them. Human subjectivity. Indeed.
Wow, going back to read, not very many good replies in this topic... I think my answer is pretty simple and what most people intuitively do anyway.