Thanks for posting this! Here's the result of geocoding the above list with geocod.io for anybody interested:

Forward Geocoding (Converting the addresses to latitude/longitude): https://gist.github.com/MiniCodeMonkey/13c02d45089478182c3d1...

Reverse Geocoding (Converting the lat/lon to addresses): https://gist.github.com/MiniCodeMonkey/13c02d45089478182c3d1...

Based on the above definition, geocod.io's accuracy for reverse geocoding of this list is 95.2%

Putting this together with dbatten's original findings, the list would look like this:

Google: 97% ($4 per 1,000)

Geocod.io: 95.2% ($0.50 per 1,000)

Mapbox: 95% ($0.50 per 1,000)

TomTom: 73%