Is your commute mostly highway? Mostly rural road?

Do you need to haul anything?

Best question: Are you going to try and max out your mpg's? Or are you just looking for a normal driving car that is better on gas?

Owning a civic hybrid I can only say its a great car for driving normally. At normal speeds I don't think either the Prius or Civic has any clear advantage. The 47/48 average mpg for both cars here speaks for that.

Things to consider could be:
- Civic still offers tax credit I think
- Prius has lower starting price if you can get a base model now, not sure how many features they removed compared to previous lineup.
- Prius is better in city
- Prius has more storage space
- Civic is refuted to be more comfortable for shorter drivers (claimed)
- Civic is less expensive to keep insured (personal research, Prius is classified as a larger car perhaps?)

I'd day test drive both and pick the one you'd rather sit in for long periods of time. If your going to drive normally then you can't go wrong with either. They will both give your wallet a break compared to a comparable gas only sedan.

Edit: Noticed your small text: I'd say neither is "great" on ice. Invest in winter tires if conditions will require it.