It will be interesting to see how the upcoming Prius plug-in hybrid fares against the Volt and Leaf. Frankfurt is less than a few weeks away. Frankfurt Awaits Debut of 2012 Toyota Prius Plug-In Hybrid
What is the criteria? We already know that affordability was given a much higher priority than Volt. We already know that both engine efficiency & emissions are better than Volt. Overall efficiency is the combination of gallons & kWh based upon real-world data. Actual consumer consumption results differ from estimates, especially when it comes to plug-ins. So the upcoming reveal won't provide that information. Sales are the ultimate measure of success, since the purpose of the technology is to become the mainstream replacement of traditional vehicles. Leaf competition does pose a challenge for gauging interest. It's easy to imagine that being a popular option for 2-car households, where the other vehicle is used for the more demanding travel. So it doesn't reach as wide of a market as the potential for Prius. Of course, there is always the measure of perception. The quantity & intensity of negative spin from the competion could provide a good indication of how worried they are after getting detail about the production model of PHV. .