The bottom line is that the better configuration depends on which driving cycle you use. For the foreseeable future as batteries remain expensive, getting maximum benefit depends how far you drive and at what speeds. For shorter driving cycles and lower speeds, the less expensive blended PHEV approach used in the plug-in Prius and Saturn Vue get the most benefit from a smaller battery. People who drive at higher speeds or longer distances will get more benefit from an E-REV like the Volt, which comes at a higher cost. The bottom line is that there is no one right answer for everyone. The replacement of petroleum will require a diverse approach to energy. The best answer will depend on where you live and how you use the vehicle.
[Source: Green Car Congress]