If we are looking for traffic StumbleUpon is the best prefer compare to Pinterest. I am looking for more traffic to my contents. So i prefer StumbleUpon.
Both have its own stand in social media world. The way to submit URL is different in both not any major difference.
Both of them has their own significance, but I think for brand promotion or for marketing purpose Pinterest is better and trustable social network than stumbleupon, pinterest can give you massive traffic easily. if you have attractive images in your website then it'll be easy to promote your product on Pinterest.
Pinterest has good value if you are promoting a product. Stumble upon is more random. Pinterest also has good traffic value. If you use metrics on it you will be surprised at how highly trafficked Pinterest can be.
Like some of the others here before me have mentioned, I think it all depends on your target demopgraphic. I think Pinterest is a major social media player for women in the demographic range of 16-65. Obviously certain industries (fashion, accessories, etc) lend themselves better to Pinterest. To be honest, I don't think I would put any effort into Stumble Upon, as in my opinion it ranks near the bottom of ideal social media platforms for small businesses.