StubmleUpon is a great in general, Delicious is good when your on frontpage like mentioned above. When you aren't there, it's simple, you get hardly any traffic. So if it was me, I'd go for StumbleUpon.
I love the stumbleupon bar, and i've never used del.icio.us so i cant really be sure Though i would say stumbleupon if pressed
I think you have a better chance of receiving more visitors with Stumbleupon. Still, both can really boost traffic if done right.
I haven't had any luck with either. I prefer sites you don't have to do anything on. I have accounts on digg and stumble but I'm not active.
I used them for my personal use.. rite now I am doing it for professional reason, still I think delicious is the best.
Agree with you but are there any more social bookmarking sites who have same importance like these two have (Stumble Upon/Delicious)
I always do bookmark in stumble upon than delicious. But, both are quite good and top social bookmarking sites. If you visit mashable dot com, you see stumble upon next to '+1'.