I get most traffic from Pinterest, but it can take several months for the pin to start gaining lots of attention. e.g two pins I posted back in August have only really began taking off in the last few weeks. I do make the effort to create attractive images using Canva which I think really helps.
Funnily enough, although I only have a few hundred followers on Pinterest (I don't really have the time to put a lot of effort into finding new followers), this doesn't seem to matter too much as my pins still get lots of views. I think it also helps to join a few really well followed boards in your particular niche and pin there.
I don't get much from Stumbleupon, Yahoo answers or Twitter. Quora can be quite good and get me a number of views. I've never used Tumbler or Instagram though so can't comment on those. I haven't bothered anymore with Google+. For me I don't think it is worth my effort.