dofollow link will bring pr juice to your site, nofollow link will make your site becomes more naturally from the view of Google. They all are important for your link building, you can set 1/3 or 2/5 for your dofollow and nofollow.
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You should always try to get an equal number of dofollow and nofollow backlinks.
Though nofollow backlinks won't pass PageRank to you but they are still helpful in getting your site crawled by the Google Bot.
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It is good to build do-follow links but no-follow is not a taboo. Do-follow give us ranking and no-follow provide us traffic so ultimately their goal is same but they are on different path.