Stumbleupon is better unless you can get to the frontpage of digg, and the traffic will probably be too much for your server to hold at once.
I only used Digg... never try Stumbleupon yet. One of my blog sites when to 1st page from 433,000 search in Google for one keyword phrases
Technically digg is a lot better for you. You get a lot of backlinks as a result. I don't think i've gotten too many backlinks from SU...
Digg will send you a lot more if you get to the front page, but I've saw a lot of traffic to my sites from StumbleUpon when they've gotten a few good stumbles.
well, digg is good for technical stuff while stumbleupon can be anything. but for all i know digg loves technical stuff. i remember kevin rose (one of the founders of digg) back when digg is not yet in the cyberspace...he's such a cutie when reporting at techtv. oh, by the way... i've heard that you can actually earn $0.5 everytime you digg or stumble and the minimum payout is $10 through paypal. PM me for the link or read my post about it. kisses!