Do some research, a REAL world peek is at fuelly.com
below is a link to civic hybrids and real world averages from real people. Remember the civic hybrid is about 3 to 5k higher right off the bat.
Honda Civic MPG Reports | Fuelly
below is a link to prius in the real world averages, all years.
Toyota Prius MPG Reports | Fuelly
and finally below we have the insight all years..
Honda Insight MPG Reports | Fuelly
as you can see not a lot of difference for mpg, depending on miles per year your cost for the difference of mpg is minor.
Now the cost of these three vehicles is significant. This was my deciding factor when I purchased. My criteria was... 40mpg AVERAGE... all the time, 50% city, 50% highway.... only 4 cars in the US will do this, period....
So with 40mpg or better and the lowest cost of ownership the answer was pretty simple to me (but I bought it outright, NO lease) and a guy I work with, I track his mileage on my fuelly.com account also.
Good luck in your search!! I agree with Brian, surely in 3 or 4 years we will have more choices for high mpg vehicles!!!