user254: Sometimes I read an answer which I don't agree with.
I could just downvote the answer, but should I post a comment as well?
If I do post comment, to an answer that I disagree with, does it matter what kind of comment I post?
Does it matter how I phrase it?
Does it matter which user I'm talking to?
What can I say, and what shouldn't I say?

user-1: If I find the answer to be factually wrong or misleading/unhelpful I point it out on a comment and downvote it (unless the overall answer is good only needs correction).
For example, I recently commented here explaining why I downvoted the answer.
On the other hand, I don't comment if I simply disagree. Also I don't comment if I disagree and I see other good answers receiving votes since sometimes it can be hard to argue why I find the answer bad, and I think it's sufficient to have good answers on top (and it may even be educative to preserve not-so-good answers bellow the good ones).
For example, recently, I had a comment in one of my answers that was downvoted. The comment was deleted and I don't quite remember it's exact content , but the commenter was just disagreeing with what I wrote. On another answer on that thread I saw Andrei explaining to him why he deleted the comment. I thought it was a good move, even though I still would have left it unanswered (for the exact same reasons, though someone else could have answered it, possibly leading to a flame war).
Another example is this answer which I don't agree, but I didn't comment on it: I find the other answers to be good and since this one is bellow all the others, I think this makes the point of a rebuttal.

user295: 
Sometimes I read an answer which I don't agree with.

If this disagreement is due to the view point is a particular school, tradition, line of thinking, or what is orthodoxy and what is not then best is to do nothing (commenting or down voting) as there might be others who would find this agreeable. Even if you downvote leaving comments might make new comers un welcome from the particular tradition.
If the disagreement is a matter of opinion the best is not to do anything again as ideally you should verify theory and practice through meditative experience and not opinions.
If it is a matter of possible error or omission, or the answer is does not seam to answer the question, by all means comment and point out the errors and also give guidance. Ideally avoid confrontational tone and be friendly.
Also keep in mind that the angle 2 people look at a question is not the same also. In this case it will be very useful to comment for every one as to there is another angle or another way to look at things. Ideally this should not be a reinstatement of your understanding. 
Also be mindful, when there are multiple answers some answers may aim to fill the gaps or points which one differ with in an existing answer or comments. In these cases not all answers will be complete. But if its the 1st then the sanded you are looking for needs to be higher, but also give it some times as sometimes the initial answer may be  skeletal answer to save what you have written so far with possibility of subsistent edits to fill in the meat when you find more time to work on improvements and references and content.
Also there are things that people take for grant that others know because of the discourses you listen very often or the temple you go often or the type of meditation you are familiarize with. These are things that slip through when you answer. This is also best pointed out in comments where you can add these information as this will improve the answers because others participating under another teacher may have no clue what you are talking about.
Local Buddhist educational and culture can also can influence certain concepts and view. There aspects of the doctrine which is taught which even I am struggling to find how to trace back to the Suttas which are available in translated form. Asking reference requests for this type of answers can be tricky as this is what we have been taught or this is the commonly held view. In these cases best is to retrospect to see if any aspect is a culture specific or commonly held view. These comments and answers can be reference to others who might not be familiar.
Also on what is topical and what aspects are given prominence varies country to country varies. E.g. topics like Tatta, Sunyatta, etc. found discussed at length in Thai sermons but hardly in Sri Lanka. So this also give some aspect of familiarity and taking for grant that the reader would know the background. Best is to leave comments for further elaboration.
Apart from commenting it would be most beneficial everyone if you add an answer with your angle if appropriate.

Does it matter which user I'm talking to?

If it is a new comer give them time to adjust. Gently point out why something is not and answer or something is like a discussion. Give them time and opportunity to adjust. We want to grow the side than drive away potential users.

254: <p>Sometimes I read an answer which I don't agree with.</p>

<p>I could just downvote the answer, but should I post a comment as well?</p>

<p>If I do post comment, to an answer that I disagree with, does it matter what kind of comment I post?</p>

<p>Does it matter how I phrase it?</p>

<p>Does it matter which user I'm talking to?</p>

<p>What can I say, and what shouldn't I say?</p>
 -1: <p>If I find the answer to be factually wrong or misleading/unhelpful I point it out on a comment and downvote it (unless the overall answer is good only needs correction).</p>

<p>For example, I recently <a href="https://buddhism.stackexchange.com/questions/12748/meaning-of-body-is-emptiness-emptiness-is-body/12749#comment21216_12749">commented here</a> explaining why I downvoted the answer.</p>

<p>On the other hand, I don't comment if I simply disagree. Also I don't comment if I disagree and I see other good answers receiving votes since sometimes it can be hard to argue why I find the answer bad, and I think it's sufficient to have good answers on top (and it may even be educative to preserve not-so-good answers bellow the good ones).</p>

<p>For example, recently, I had a comment in <a href="https://buddhism.stackexchange.com/a/12663/382">one of my answers</a> that was downvoted. The comment was deleted and I don't quite remember it's exact content , but the commenter was just disagreeing with what I wrote. On another answer on that thread I saw Andrei explaining to him why he deleted the comment. I thought it was a good move, even though I still would have left it unanswered (for the exact same reasons, though someone else could have answered it, possibly leading to a flame war).</p>

<p>Another example is <a href="https://buddhism.stackexchange.com/a/12761/382">this answer</a> which I don't agree, but I didn't comment on it: I find the other answers to be good and since this one is bellow all the others, I think this makes the point of a rebuttal.</p>
 295: <blockquote>
  <p>Sometimes I read an answer which I don't agree with.</p>
</blockquote>

<p>If this disagreement is due to the view point is a particular school, tradition, line of thinking, or what is orthodoxy and what is not then best is to do nothing (commenting or down voting) as there might be others who would find this agreeable. Even if you downvote leaving comments might make new comers un welcome from the particular tradition.</p>

<p>If the disagreement is a matter of opinion the best is not to do anything again as ideally you should verify theory and practice through meditative experience and not opinions.</p>

<p>If it is a matter of possible error or omission, or the answer is does not seam to answer the question, by all means comment and point out the errors and also give guidance. Ideally avoid confrontational tone and be friendly.</p>

<p>Also keep in mind that the angle 2 people look at a question is not the same also. In this case it will be very useful to comment for every one as to there is another angle or another way to look at things. Ideally this should not be a reinstatement of your understanding. </p>

<p>Also be mindful, when there are multiple answers some answers may aim to fill the gaps or points which one differ with in an existing answer or comments. In these cases not all answers will be complete. But if its the 1st then the sanded you are looking for needs to be higher, but also give it some times as sometimes the initial answer may be  skeletal answer to save what you have written so far with possibility of subsistent edits to fill in the meat when you find more time to work on improvements and references and content.</p>

<p>Also there are things that people take for grant that others know because of the discourses you listen very often or the temple you go often or the type of meditation you are familiarize with. These are things that slip through when you answer. This is also best pointed out in comments where you can add these information as this will improve the answers because others participating under another teacher may have no clue what you are talking about.</p>

<p>Local Buddhist educational and culture can also can influence certain concepts and view. There aspects of the doctrine which is taught which even I am struggling to find how to trace back to the Suttas which are available in translated form. Asking reference requests for this type of answers can be tricky as this is what we have been taught or this is the commonly held view. In these cases best is to retrospect to see if any aspect is a culture specific or commonly held view. These comments and answers can be reference to others who might not be familiar.</p>

<p>Also on what is topical and what aspects are given prominence varies country to country varies. E.g. topics like Tatta, Sunyatta, etc. found discussed at length in Thai sermons but hardly in Sri Lanka. So this also give some aspect of familiarity and taking for grant that the reader would know the background. Best is to leave comments for further elaboration.</p>

<p>Apart from commenting it would be most beneficial everyone if you add an answer with your angle if appropriate.</p>

<blockquote>
  <p>Does it matter which user I'm talking to?</p>
</blockquote>

<p>If it is a new comer give them time to adjust. Gently point out why something is not and answer or something is like a discussion. Give them time and opportunity to adjust. We want to grow the side than drive away potential users.</p>
