I think Facebook is best and then the twitter and then the Google+ because for me Facebook had More traffic than in twitter and Google+.
I think Facebook is the best of the best, Google+ is not strong enough, though Twitter is becoming very popular nowadays.
Sir I Think Google IS The Best the Google Site IS Very Big And Very Nice Site Google Search And Then Facebook And Twitter So Sir Google Is The Best Web Site .
Facebook is best for me because of it's features. It allows me to advertise, promote and at the same time connect with my friends and prospects.
I prefer Facebook because I have used it for the longest as far as social networks. But for me it depends on what you use the 3 for. And we should be looking out for the new.myspace.com and its new features et cetera then lets come back and have another discussion.
Without knowing more about what you are promoting I'd have to say that Facebook is really the all around Social Media giant right now. They're great for promoting content, products and more...making them a good place to focus on.
Facebook is a social site beside Google is the best Search Engine and Twitter is best for your opinion. Both are well and good for me.