In short, commenting will not help you. It may drive a few hits here and there to your site, but search engines will not consider those links as authoritative links.

Nearly all links on blogs within the comments are nofollowed to help with moderation of the web as a whole.

if you have something valuable to say on a post, you ought to leave a comment -- but do not go around from blog to blog leaving worthless comments as it is just a waste of your time.

Say something of value and if other people also see it as valuable, they are likely to read your blog and link to you with a real link.

Quality over quantity.