depends, best for what? Best for getting traffic directed to your site? I like MyBlogLog to beggin with (for initial traffic) Best for contacting friends? Best for gaining inbound links to your site?
stumpleupon and digg sends plenty of traffic to my sites but my revenue never increases with the traffic so I wouldnt consider it great traffic
Digg is the best IMO. Stumble Upon traffic is quick and doesn't monetize at all for me - they stumble and get lost quickly.
Their are many sites but this depends on friend list also . If you are new than no one will work for you , so spend some time on them and than you can get some good profit from them . Here is the list of some good social bookmarking websites which have pr7 to pr9 . Top 15 social bookmarking sites
start by submitting to the big ones out there and see what traffic you get and see if you can turn that traffic into repeat traffic. Digg, Stumbleupon, Propeller, Mixx.
Try my list List of “Do Follow†Social Bookmarking Sites This is all Do Follow aside from traffic it can also help in your SEO..
No there are social bookmarking sites that are not do follow... Check http://socialmarker.com/ and you can see some popular Social Bookmarking sites that are No Follow
Best for gaining traffic are stumbleupon and digg, but running the gambit is the best to gain back links.
For traffic, I get good results from Digg and Propeller and it helps you get your new content indexed fast. Also, try Plibb.com, which is a do follow site. I just opened it but it is starting to get some decent traffic and I offer revenue sharing as well.