Here's my rational behind the insight. Feel free to disagree

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The Insight is smaller, and lighter than the Civic hybrid, but gets less MPG. Why you ask?
WELL... while doing research, it was a main selling point that the insight be cheaper than the Prius. While doing this, they happened to cut a lot of corners, which resulted in the lower MPG- but you have to quesiton, with that logic, how efficient is the rest of the car in the end?
I would choose the Prius because Toyota was the first to mass-market a successful hybrid car, so they know what they're doing when it comes to hybrid technology. Since they have that solid background in hybrid technology, each generation is only improving, while the other brands are still developing, therefore you get a more advanced car.
The Insight is actually is also really weird when you drive it. To save gas, the car actually shuts off when it comes to a stop, so you have to be pretty gentle when you accelearte (this is when the engine turns back on), or else your car will feel like it's hurdling.
Just my two cents on the subject. In the end, TDI Diesel>Hybrid batteries that kill the enviornemtnt with their toxic waste