I like twitter the best, because it is easier to software or automation sites to post to such as socialoomph. Seems I get more traffic from twitter than facebook with less effort. Just my 2 cents.
Facebook and Twitter is still the best for me. I know both facebook and twitter will add a valuable help to increase your traffic and esp in promoting.
Every sites has it's own features which make them different from each others. We can't compare but to use their positive points. Btw you know there's a website with every features of top social website and more special features for the people in our society. I mean needy people. If you wanna know more about Corlif, just visit the link at my signature. Thanks
Of course its Facebook, aside from being widely use it is also an effective way for business and advertisements