Who should post an answer? The first one to post an answer.
Comments are not unhelpful, but they are "second best" on SE sites. First of all, they are likely to get deleted eventually. An answer won't, unless it is really bad, or "spam." Second of all, an answer can be upvoted (or downvoted) a comment can't (except in extreme cases connected with "flagging). Basically, an answer represents content for the site, and meets the sites objectives.
So don't be shy, if you have something to say, say it. If you feel that one of the other posters knows the subject better, you might say so and let him or her have the first crack. But if s/he doesn't, you should step into the breach.
In my family, for instance, my sister is by far the better pianist. But I am the one who plays the piano in public.