From my point of view digg is better than reddit because digg have some popular categories and helpful for users and digg is use more than reddit.
Both of them are effective traffic sources for SEO. But personally I prefer Digg as a user since the full-of-words page of Reddit always make me dizzy...
They both are really gives handsome amount of traffic to our website but digg is much more famous than reddit due to its familiarity it is being used more than reddit.
I am looking for someone who can provide guaranteed "diggs" or thumbs up on reddit to reach the home pages. If you can help me, Im willing to pay, send me a PM.
For me Digg, however I have spent quite a bit of time using reddit recently trying to get it to the standard as my Digg account. It depends how much work you put in in my opinion
If working effectively on social platforms, you will get success not only from Digg or Reddit, but also from other sites like delicious, SU etc..
My Digg backlinks always seem to get noticed first by Google for some reason. For that reason, I would have to say Digg is the better choice, but Reddit is great too. Don't limit yourself with social bookmarking. Submit to all the big ones if you are trying to get backlinks and some decent traffic.