Blog commenting is not a direct approach to a link. In other words majority of comments you make will allow you to place a link as your name (tip: use your name or company name), This is usually a no follow link which does not count for SEO. However, if you build relationships with other by commenting/contributing (adding value) on their posts (make them your friends) and interacting with them you can earn good quality links and mentions to your site/articles.
If you read an article and you disagree with it or want to add a bunch more value to it, you can write a post on your blog and in the comments of the article you want to contribute to you can leave that link. Although it's a no-follow link it adds value to the user and they are more likely to share it or link to it.
and tries to be good...