Twitter for me because I am using twitter to read some twitts from different famous people and it was really fun to read those twitts from them
Actually Twitter and Digg both are useful where Digg is helpful for social bookmarking and twitter is actually a micro blog. But if I need to compare between them then I must say Digg helps us more to get target traffic to our site. Also sometimes it helps us a lot in quick caching a page in Google.
Still Digg get more votes in comparison of Twitter......
My vote also for digg, I find it a lot more useful than Twitter.
At the moment Twitter is more useful for me. I was an early adopter and therefore have an alright following. It provides some quite valuable traffic and connections with other marketers.
I'm waiting for the new version of Digg