both are great... in my case i get more traffic from SU then DIGG... but i use digg to have permanent link for google.... but m sure if you are only looking for traffic stumble can give you lot more than digg.
It is better if you have rich content in it.. and the most important thing about driving traffic is stumble the pages which you have posted in any of the known social book marking sites. Good Luck !
I agree soon as I digg a story it is on the home page og Google most of the time with in a day or two.............
i think Stumbleupon is Internal Search but Digg is External Search in Google so Digg is better than stumble in Search engine and stumble better than Digg Giving a Lot of Traffic
thats impressive observation Ihave to be honest stumble doesn't convert the way digg does, I never see stumble on the serps?? the way Digg does I wonder why??/
Everything depends on your activity buddy . Use any site but what you will get is reciprocal . If you want to promote your sites than always check that if you will digg and stumble others than they will yours .
Digg is good..I used it for a long tail keyword and I am on first page in 2 days from that..It is trick if you use digg for long tail and then you will be on first page for that long tail in a day...not waiting for a week even.. But I am little bit new to this field I don't know it is a Black Hat or White Hat trick But I think I used it smartly not spamed anything.. )
From a traffic viewpoint, I get more from stumbleupon.com than digg.com. But I do submit my sites to both. Like everything in SEO, content is the key
Many SEO Masters says that when it comes to Traffics Stumbleupon is the best and the sources of traffics according to SearchEngineNews.com.
digg is great sb. it gives dofollow links and u can submit every page. stumble is a lot better for traffic though imo. but stumble works better for entertainment purposes.
I think, stumble is better than digg. But, you have good circle and reviews to ur site. High reviews, generated v.good traffic to ur site in Stumble. All the best.