More efficient vehicle for what?

For most people, the hybrid will get more gas mileage than a similarly sized gas vehicle so you use the hybrid for transporation. And if the hybrid is indeed more fuel efficient at generating electricity, too, then I can see the logic of reserving all your available fuel, from both vehicles, exclusively to the hybrid.

But if there's not much appreciable difference in power generating efficiency, in that case, it would seem to be logical to use the hybrid for driving and you can simultaneously run the gas vehicle for power back at home, if you want. In this case, you'd theoretically still use the same amount of fuel overall as you would if you just used the hybrid for transportation and all driving.

And while I'm asking, I might as also ask, so just how many angels can dance on the head of a pin?