As per my knowledge do follow and no follow both are useful but do follow is more benifical and useful because google consider do follow link very quickly. And there is less chance for no follow to be considerd by google.
Probably the right answer was given all ready. What I want to add: sometimes you can place a link on site even if it is no follow as you are interested in real people to visito your site. A visitor will click a link if it likes where he will go ( not if it is do or no follow )
Both DoFollow Links and NoFollow Links are good for your Websites.we can say that Do-Follow Links are good for Human Traffic and SEO Traffic.And on the other side, No-Follow Links are only good for Human Traffic which is still the best traffic you can have.
Nofollow and dofollow both links are good. Dofollow links are better than nofollow links. Dofollow links are used to increase the website ranking and traffic. In the other side dofollow links are used for improving the website traffic only.