I am going to say that out of the two for long term effectiveness that article marketing is better for building links.
Why? because most social bookmarking site's use the nofollow tag so the main benefit with social bookmarking (imo) is the instant traffic you get from it and some times it can be quite a large volume. Most long term effects from social bookmarking sites will fade once the bookmark becomes old.
Article marketing on the other hand build you actual backlinks without the nofollow tag and these links just build over time. Now you can tell which is better, there is also a lot more work involved in good article writing compared to submitting a link to a social bookmarking site.