Mix cloud or sound cloud?

I can't talk for Mixcloud but from my experiences with Soundcloud, Soundcloud's customer care is very good. Also Soundcloud's App for Mac is a handy tool!

I use Mixcloud for my mixes based on the mechanical vs broadcasting license issue mentioned earlier. It's really easy to export the tracklist out of Traktor and then mark the tracks. If I was producing original stuff I would use SoundCloud.