Test drive them first! I test drove a Volt, C-max, and (non plug-in) Prius all in the same week last year. Volt was the best, even though I was totally unfamiliar with the layout and feel of an American car, having mostly driven only a Toyota and old Mazda in the in the past.
We ended up buying a 2012 Volt last year and love it still. It handles well and is comfortable. Seats do not fold flat in the back, but they do fold and allow for a pretty good amount of hatchback cargo. It has a kind of clever heating system. When it is REALLY cold, it will fire up the gas engine even if you have a charge. It will run 2-3 minutes, then switch back to electric as you drive. I have only had this happen a few times; I guess it depends on the climate where you live. Also, we have a car port and not a closed garage, which may make a difference.
Hopefully the Volt will eventually be our only car. We have already taken it on 2 road trips with no problems.