Hello frndz.. Yes I agree with all, Only dofollow blog commenting is beneficial for Google Rank... Thanks
I agree that do-follow blog more benefits for our blog commenting link but it does not mean that blog commenting are useless because no-follow link have also his benefits like our keyword will be high in Google search and if any visitor is reading blog,may be he will also read our comment and used it to reach our site.
Blog comments are a good source of backlinks. The key is to get quality links. Links on pages related to your niche, with high PR and not many outgoing links.
dofollow links are quite useful as blog comments. I would say nofollow links are also good as they might bring traffic to your blog/site. Maintain a proper strategy.