Both provide your similar kind of backlinks but whether you get backlinks from directories or social bookmarking sites, you should avoid building links on fresh directories and bookmarking sites and only use those directories and bookmarking sites which are running at least for more than a year.
directory submission is taking time to be listed, but social submission is giving backlink at the time of the submission and
most of the social bookmarking sites you can create your profile also and get the backlink from there also.
From my personal experience, submitting website to web directories may result in receiving filter in google for website on keyword you've submitted. You need to be very careful with selecting web directories you're submitting websites to, and they shouldn't be your main source of backlinks, I would say no more than 10% of it.