user2697: After 1.Nf3 I can gain space with either of 1...d5 or 1...b5. Which of these two is better?
I presume it's 1...d5, but I just want to make sure.

user19861: Objectively 1...d5 is better because it grabs control of the center. 
Practically, most people will respond to 1. Nf3 with an opening they have worked out and are familiar with even if it is not objectively best. 

user6966: This is hopefully the answer you're looking for, Nf3 is part of 2 Openings (as far as I know).
First is the "Zukertort Opening" 1.Nf3 d5 (so d5 is the response) however there is also a c5 response for black attempting to make it a Sicilian (I do not know much about this opening except for this you'll have to do some research on it)
Now there is the more famous Reti Opening, where it's actually 1.Nf3 d5 (just like the last one) and now 2.c4... You'll most likely find a lot more information on this opening than the Zukertort.
So the overall conclusion 1. Nf3 d5 is the answer for your question, however as you can see there is the c5 answer as well. So it depends on your play style afterwards. You might want to play the c5 from the Zukort to transcend into the Sicilian (which might be up your alley depending on how you play as black)
Hope I helped. If you have any further questions feel free to comment and I will answer to the best of my abilities.
Also just to make sure, those are the only 2 openings I know of that start with Nf3 there might be others :) I will research around and see if I can find any with other answers then post a comment on this post :)

user4362: After 1.Nf3 the most popular answer is 1…Nf6, which is a hundred times more common than 1…b5. 1…d5 is the second most popular choice, still fifty times more likely to appear on the board than 1…b5.
Now the difference between 1…Nf6 and 1…d5 is mostly one of compatibility with the rest of your opening repertoire. 1…Nf6 is more common because the indian defences are more popular than the 1…d5 against 1.d4.
But 1…b5 is decidedly offbeat. The reason is that it doesn't immediately fight for control of the central squares. The importance of the central squares is explained in the answers to this question: 
Why is the centre of the board considered important in chess?
Still, 1…b5 isn't a mistake. It has the ideas of developing the bishop to b7, making c4 impossible and maybe annoy a Nc3 in the future. If black can consolidate, the additional space on the queenside might make a difference.
The main problem from a theoretical standpoint is probably that it is rather slow: 1.Nf3 b5 2.e4 Bb7 3.Bxb5 Bxe4 4.Nc3 Bb7 5.O-O and white has quite a significant development lead.

2697: <p>After <code>1.Nf3</code> I can gain space with either of <code>1...d5</code> or <code>1...b5</code>. Which of these two is better?</p>

<p>I presume it's <code>1...d5</code>, but I just want to make sure.</p>
 19861: <p>Objectively 1...d5 is better because it grabs control of the center. </p>

<p>Practically, most people will respond to 1. Nf3 with an opening they have worked out and are familiar with even if it is not objectively best. </p>
 6966: <p>This is hopefully the answer you're looking for, Nf3 is part of 2 Openings (as far as I know).</p>

<p>First is the "Zukertort Opening" 1.Nf3 d5 (so d5 is the response) however there is also a c5 response for black attempting to make it a Sicilian (I do not know much about this opening except for this you'll have to do some research on it)</p>

<p>Now there is the more famous Reti Opening, where it's actually 1.Nf3 d5 (just like the last one) and now 2.c4... You'll most likely find a lot more information on this opening than the Zukertort.</p>

<p>So the overall conclusion 1. Nf3 d5 is the answer for your question, however as you can see there is the c5 answer as well. So it depends on your play style afterwards. You might want to play the c5 from the Zukort to transcend into the Sicilian (which might be up your alley depending on how you play as black)</p>

<p>Hope I helped. If you have any further questions feel free to comment and I will answer to the best of my abilities.</p>

<p>Also just to make sure, those are the only 2 openings I know of that start with Nf3 there might be others :) I will research around and see if I can find any with other answers then post a comment on this post :)</p>
 4362: <p>After 1.Nf3 the most popular answer is 1…Nf6, which is a hundred times more common than 1…b5. 1…d5 is the second most popular choice, still fifty times more likely to appear on the board than 1…b5.</p>

<p>Now the difference between 1…Nf6 and 1…d5 is mostly one of compatibility with the rest of your opening repertoire. 1…Nf6 is more common because the indian defences are more popular than the 1…d5 against 1.d4.</p>

<p>But 1…b5 is decidedly <strong>offbeat</strong>. The reason is that it doesn't immediately fight for control of the central squares. The importance of the central squares is explained in the answers to this question: 
<a href="https://chess.stackexchange.com/questions/5142/why-is-the-centre-of-the-board-considered-important-in-chess">Why is the centre of the board considered important in chess?</a></p>

<p>Still, 1…b5 isn't a mistake. It has the ideas of developing the bishop to b7, making c4 impossible and maybe annoy a Nc3 in the future. If black can consolidate, the additional space on the queenside might make a difference.</p>

<p>The main problem from a theoretical standpoint is probably that it is rather slow: 1.Nf3 b5 2.e4 Bb7 3.Bxb5 Bxe4 4.Nc3 Bb7 5.O-O and white has quite a significant development lead.</p>
