Either way, I'm gonna stick to Chromecast. It lacks mirroring capability, but it's a true smooth performer when it comes to Netflix and Google Music. Miracast worked excellent for watching pictures I took with my Nexus and sharing them with friends and family. Hoping that capability will come to Chromecast in the near future. But Miracast can be a good contender if they develop it further and work out the bugs.
The technologies are very different as Chromecast gets the audio/video directly from servers and Miracast gets it from the Android device. Hoping more developers will make apps for Chromecast.