To directly answer your question:

The Civic or Prius will perform admirably provided that the freeway regimen you mentioned (10-20%) remains true. The reason why is because the bulk of your remaining driving will occur at slower speeds (45-50MPH) which is where the Civic really shines and the Prius is also excellent. If the urban content of Stop and Go is higher and the average speeds are even lower, then the Prius is the undisputed champ.

I assume the reason you asked about the Prius and Civic is because you want the best "money saving" opportunity, fuel economy and emissions performance.

-You can expect to obtain 45 to 55 from a Prius II (and much more if you drive by its instruments)
-Expect 40-50 from a Civic Hybrid II (and more if you drive by its instruments)

The other vehicles mentioned by the previous posters are excellent as well, particularly if they fit and address your objectives, needs, and tastes. Only in such a case, would I not hesitate backing their recommendations.

Cheers;

MSantos