Hi, It doesn't matter if it is a do follow or no follow social bookmarking site. Important is that you are aiming for a huge number of traffic to your site. Social bookmarking is a very great technique to bring traffic to your site.
Both are good to get traffic...& i don't think so, generally we do bookmarking for link building purpose...What do you think???
If you want to index your page more quickly and if you want a search engine to come more rapidly as your content is updated daily then you go to social bookmarking and pin up your pages on high pr social bookmarking website. Other advantage is of course to drag more and more traffic to your website. Keep book marking to be up to date in Search Engine.
Make your social bookmarking strategy be balance. Even the do-follow or no-follow will do for you but the site must have a reputation and high PR.
Both do-follow and no-follow are helpful but do-follow is better .Social bookmarking always good for seo .
IF you are thinking to bring only traffic to your site using social bookmarking sites, than it does not matter if that link if do foloow or no-follow as they both bring traffic to your site. But if you are looking from back link point of view than definitely you will have to go for do-follow social bookmarking sites.
Dofollow are more important but nofollow also help in your ranking. Yes its true Digg provide nofollow links but some others search engine also pick that links.