I am appreciate with your views both no follow and do follow links are help us to link build .But do is the best way to improve traffic for our site and no follow also help us to increase traffic. In particular case like blog commenting only need to use the do follow link.
Nofollow refers to a link attribute that allows website owners to tell search engines that a particular link does not confer credit to the target site. The site is crawled but not indexed in google's index.While it's a no follow link you cannot get the link juice.
Do-Follow link has a great value to all search engines and to increase Google page rank o-follow links are very helpful. If you want see your site in the first page of search engine then you must increase do-follow links.If its a dofollow link crawler can crawl that link and some link juice can be passed.