I don't use any of them because I think that you can find useful stuff trawling the Internet by yourself.
The older I get the less interest I have in hearing what people without any visible track record have to say. Also, havng a track record does not necessarily signify that those people have anything much to say; you know, that picture vs the thousand words thing?
Language seems to be a disappearing entity - maybe the world is preparing itself for the time when we live by instruction and emotion by implanted chip. That will be fun. Perfect communism at last: no arguments, no wars, no nothing.
Rob