We recently did a comparative analysis of cloud speech-to-text providers for a project. We looked at:

1. Google Cloud Speech API

2. Microsoft Bing Speech API

3. IBM Watson Speech to Text

The ranking was as listed above but we had real challenges working with call-center audio recordings. The quality was less than idea but still very clear. We saw a huge reduction in accuracy compared to in-browser testing. Additionally Australian English is particularly not solved.

Because Google's API isn't currently doing speaker-detection, we looked at using Watson's speaker-detection as a secondary step but found it too complex and error prone. There is definitely room for a startup in this area and it also needs continued investment from the bigger cloud providers.