I like myspace as I get traffic from it probably because I have several thousand friends doing the same as me. Tried perfspot as the links are live not blocked but they delete your account if you add too many so its not an easy one. I tried Digg and Stumble but didnt do very well with them probably becasue I didn't really know what I was doing (and still don't)
digg and propeller is the best for social bookmarking site i have submitted these 2 sites after that i got more traffic
Definitely digg and propeller. Even articles with 1 digg get some traffic from these sites. However you might be better off submitting to many popular sites rather than sticking to just one site. While you might get less traffic from each individual site the total traffic might add up to more than what you get if you just concentrate on one site.
Most people would say stumbleupon or digg but I still prefer backflip, bibsonomy, linkagogo and mister-wong because they are dofollow social bookmarks.