Okay i've started the poll so vote for it! My vote for DIGG! Perhaps there are some more article submitting sites which will give you some huge hits but right now i am preferring only 4 of them.
From what I have seen personally, it depends on the niches. Technology related niches always do well on Digg, while general interest niches do well on stumbleupon and Reddit.
Actually Digg comes first on my list as it dramatically increase the potential in visits. Afterthat, Reddit always!
buddhism, spirituality, theosophy, wisdom quotes It's no secret. Anyhow, I imagine for most niches stumble works better. It's the tech-savvy niches that Digg works best for. That may seem like the majority of the web to many geeks and DP members, but for content sites in general stumble is way better.
Technically, DIGG is the best for trafficking, but it's only in case you succeed on DIGG. As you know, it is very competitive, and it takes a lot of effort to get your story into 5-10 top ones. So, it makes sense to post regularly on each of them. And if you're feeling that DIGG is not working out for you, I suggest switching to some other, less competitive article submitting websites.
Digg for sure. They don't call it the Digg effect for nothing. I haven't had a site go down because of the other 3 but when I hit the front page of Digg, my site went down too fast and it wasn't even worth it. That's why I have an actual server prepared now.
I agree, in fact on digg there is actually no real place for many topics other then maybe their 'weird news' but then, I personally find nothing weird about your niche. I use Stumble & Delicious, but then I use Delicious as it's simply a fantastic way to add little used bookmarks. I have hardly had any traffic from it... Stumble I've had hundreds of hits.