In my experience, Digg requires a strong account to get a lot of traffic from. You can pop a link to the front page of Reddit with just a clever title.
Only ever used Digg as it always was the 1st site i would use to promote a new website,but its not as good as what it was.
Both are almost same but for me Digg is working well in terms of traffic than Reddit. Reddit looks rubbish for me nowadays.
I like reddit because it will give you huge amount of traffic with a little attention towards title but digg need some really hard work to get traffic.