I think digg is the best, but I think that's because I've grown accustomed to it, and I tend to stick with the familiar.
I stick with Digg because I think its a lot easier to read then Reddit. I got confused while trying to look at the news on Reddit.
I don't use English news sites, because it's not suitable for me, that's why I use ukr.net, ukrainian site which grabs news from almost all ukrainian and worldwide news sites.
And for sports news I go to sports.ru, biggest resource in UIE for sports.
I use facebook.
I guess the only reason why I am using it, is because I actually live in a really small town, and everyone around here only uses facebook.
I used to use Myspace before I moved, but once I found out everyone in my new town used facebook, I made the switch.
I do still use my myspace, but only to talk to very few people in the place I used to live.
I guess it just depends on what everyone uses in your community.
Stumble... I enjoy it....
Stumbleupon is the best one for me. It's very easy to use... and you can discover lots of new sites.
I don't really frequent any news sites. I hang around enough message boards that all the interesting links are picked out and given right to me with no effort on my part.
I have used Digg, reddit, stumbleupon and few others, but honestly none of them succeeded to keep me interested after a while. Google news and google reader are the best for me any day!
I'm not really into those news sites and whatnot. I use facebook, but .. well i only use that for finding local metal concerts to go to, and to get pics of my cousins kids and whatnot. But other than that, i try to avoid em. I'm just not bothered enough to use them.
I just like digg the most. But I rarely visit those social bookmarking/news sites. They are like just a place for me to promote my website(s). But I do visit digg the most because there are some really interesting things there. Other websites like reddit, delicious never interested me that much.