I really like Indigo - it seems to work very well indeed. I intend to install 8.1 on my Icon when I get home (yep, I'm in the preview program) and see how Cortana works out. It should be interesting to see how well it works vs Indigo.
Oh yeah, I forgot I was going to do this! I can tell you that Cortanas voice recognition is excellent - I don't know if she's using the same engine as everything else on WP though. WP has always performed best for me at voice. Way better than Dragon on Android or Siri.