Use them both. However unless you article is really sharp your traffic increase will not e great. Oh and unless you are a really active member of digg (read large group of clicky mates who will vote for any old toss you submit) then your traffic from that will be small, digg is not the generator it once was unless you have something really unusual to post.
In Digg, you will need to socialize and make friends with others so that people will visit things that to "digg" oftenly. It is about relationships. The more friends you made, the more traffic you will have for your "digg" stuffs. Ezinearticle is different, you don't have to make friends. Other articles directories, webmasters or bloggers may just take your essay from Ezinearticle to put them on their sites. Naturally drive traffic to your site.
Ezinearticles.com is one of the most popular article submission directories. If a topic is hot, submitted articles can get hundreds or thousands of views mainly because Google ranks pages in Ezinearticles.com highly. One-way links in the article resource boxes trickle some of this traffic back down to the writers or submitters site.
Digg if you can get enough "diggs" is useful but it depends on the niche. For Clickbank Products I prefer Ezinearticles because they have a category for my niche and do not let everybodys article pass.
Ezinearticles.com will generate quality traffic of those who are eager to learn from or get info from your site or blog. But digg bring ine more traffic but without making you a penny. Continue using ezinearticles and other top article directory for they will give you profits.