Image by jerandsar via FlickrHere are the networks that work well to attract traffic, in the approximate order of how many followers they attract. Also, a small explanation of why the work (or not) is included to the side.
1. Twitter: In my opinion, Twitter is the "gold standard" when it comes to attracting traffic to your website. In general, I count on a minimum of about 1 viewer per 1,000 followers per day, assuming that I update regularly. If you have more engaged followers than I do, you'll probably have more hits from them too. In any case, Twitter is a godsend for blogging. I actually get about 33-50% of all my daily traffic from Twitter, and I only have about 20,000 followers.
2. Facebook: The Facebook account that I have associated with my blog is relatively newer, but I'm still seeing good results from the initial trials. With only about 200 friends, I'm seeing about 2 hits per day originating from Facebook -- results even better than Twitter per capita. Of course, if you have friends and family on your blog Facebook page (as opposed to strangers), I would expect that you would see higher traffic from this. However, Facebook is still below Twitter in my estimation because it's much harder to add new followers -- meaning that even a lower rate of click through from Twitter will win in the end through sheer volume.
3. Digg/Reddit: It depends on which "camp" you're in here (team werewolf vs. team vampire guy anyone?) but both services are marginally successful in driving traffic to a blog. Both have problems, however. In the case of Reddit, they like to block users who submit a lot of articles to Reddit from a blog, and they are difficult to deal with in general. Also, the interface sucks rocks. For Digg, they have a much cleaner interface and are much more lenient on submission, but they send a lot less traffic to a blog per article submitted. I guess which one (or preferably both) of these sites you use depends on your approach to blogging. More articles -- Digg is better. Fewer, higher quality articles -- use Reddit.
4. Myspace: In theory, this dying giant of a social network site should send lots of hits to my blog -- in theory. In practice, my 1,000 plus followers have generated very few hits for my blog -- probably because many of them no longer use the service.
5. Stumbleupon: I have blogger friends that swear by this, but I've never seen a large number of hits coming from that site. For each article I submit, I can usually expect a maximum of five hits to my blog from that site, I think that the problem here is that they receive such a high volume of article submissions that most of your articles are never "stumbled upon" by the site's bots.
In summary, all social networks are good to some extent to drive traffic to your blog, but some are better than others.
