Search engines are clever now to identify the difference between links compared to 10 years ago. Top search engine like Google dedicated to provide better search results to the users. So, they will keep on adding more factors to calculate quality of the site to show better SERP results for each search made by users. There are over 200 factors involved in calculating SERP ranking for now. It may reach 300 factors soon. Of course, we can’t neglect on site SEO. This is the basic of all SEO. Going after offsite SEO like link building without proper onsite SEO will not only show poor results, sometimes it may even show any changes.
So, before go commenting on blogs or employing any other link building campaign, try to check your onsite SEO checklist. It is wise to have onsite SEO optimized site to get better benefits from search engine results page ranking from Google or any other top search engines. You can get some valuable advice from webmaster forums on section of onsite that need changes. Assuming you has done all onsite SEO without overdoing it (i.e.; stuffing keywords or giving nofollow links to all internal pages).
Now, comment on blogs that is relevant to your niche. Even though, the blog is dofollow and have higher PR (PR5+), you need to find only relevant pages to comment to get higher benefit from your backlinks created from commenting. The relevancy factor is getting stronger highlight each year as most search engine tries to give heavy weight of benefits in terms of SEO to it. So, do not waste your time hunting irrelevant links. Comment on pages that are related to your industry. If the pages is dofollow blog, then you are getting the true benefit of dofollow comment.
Next, say goodbye to auto submitter tool. I believe there are tons of free and paid tools that do auto submission of comments on your preferred blogs. It can also find relevant and dofollow blog pages to comment. Usually, this tool will only spam quality dofollow blogs which will force giving webmasters to turn off dofollow plugin. Auto submitting will also led your site caught in Akismet spam filter and will trash your comment even if you are submitting it genuinely without using auto submitting software now. Most dofollow blogs uses Akismet spam filter to help them reduce spam issues.
Google hates automates comment submitting tools. It creates huge number of duplicate content in wide range of blogs at very short period of time. It consumes considerable amount of time to crawl, index, check duplicate issue, remove from index and issuing penalty for serious offenders. Most of the users who use auto submitter tools tend to get Google penalty and will eventually give up on the domain they have been working. It is not easy to lift Google ban or penalty. So, keep your commenting activity at moderate level and post comments on highly relevant pages.