Let me give you some points from what I see daily about blog comments:
1- Many websites now have turned the link attribute in comment box to no-follow and that means they have kind of feeling that people are always use comments to spam. Unfortunately this bad feeling has also infected Google. So I do not think google will consider comment link too much but I do not think on the other side they will ignore it completely.
2- Second point many sites now require you to have an account or "sign in" via social sites in order to comment. This is another sign that traditional comments can contain bulk of spammy link. so sites owner and google want to avoid such spammy comments via compulsory login to be able to to comment.
3- If you are going to add comment then I advise you to stay away from sites that look spammy, for example when you see 500 or 1000 comments, in many languages
this is for sure spam so avoid such posts. Try to find great site and add great comment.
add comment that add plus value to the main blog post or to follow comment under it.
- If you want to add link within the comment box, then I advise you first to contact the site's owner and get his/her acceptance.
- some sites may not allow to put full blog url in the website box, so you can check this matter with the site's owner as well.
- When you contact the site's owner for link permission, this will build trust between you and the site's owner. I think if the site's owner finds your comment and your link helpful, they may make it "do-follow" in case the comment tech system is build no-follow.
- Question: will no follow help? Simply yes
Let me ask you this: Imagine you are writing about solar system for home, which is better for you (one no-follow link from NASA, CNN, BBC ....ets) OR (10 do-follow links from zero readers spammy site)
So focus on quality content, if people find your content of high quality then people will share it on social sites, on their blogs, curators will curate your content, and you will gain more traffic and more real good backlink.
At the end of the day think of quality not quantity.