Forum posting is the quickest, followed by blog comments but for shear numbers it has to social bookmarking.
Quickest would be buying a link in someones signature. If you can get someone who has 1,000 posts then that's a pretty easy way to do it and fairly cheap. It will take quite a long time if you had to sit on a computer and write 1,000 posts.
Social Bookmarking is the best way for getting one way llinks. some bookmarking sites are really very good for getting backlinks and traffic such as Digg, stumbleupon, reddit etc.
I think all of the above. Everybody agree on same things of the places to get back link. But I also would say it might not be the answer of is it the fastest?
Just remember, fastest and most valuable are not the same thing. I hope my competitors will read this thread and follow all this great advice.
Definitely forum posting and blog commenting. You can easily post three times per day across five dofollow forums, and that's 15 backlinks right there.
I do my submitting each link to etleast 10 social bookmarking sites.Though it take minimum 20 minutes to submit to all these sites,but with in one day i get the link in google from the referred site.
@Li Weng I agree and you copied my statement almost word for word: jpearce's comments: social bookmarking, blog commenting, forums. Nice work. In order too.
I wouldn't go with directory submission for fast traffic. They take forever to be approved and maybe get rejected. Directories are great for long term traffic.