Modena or Ferrara

Been to both. I'd probably return to Ferrara.

Ferrara. Use www.viamichelin.com/web/Maps for things to do (click "Tourist sites" button).

Ferrara - just watch for bicycles. Seems like more than anywhere else that I have been.

I love Ferrara, I return there every year or two. Have you been to Ravenna?

I'll give a nod to Ravenna as well. The mosaics are outstanding. I visited yesterday and when I walked into the Basilica of Saint Apollinare Nuovo I actually stopped dead in my tracks staring at a mosaic that must have been over a hundred feet long. The sights are a short walk from the train station; there are frequent departures from both cities and travel time is between 1 hr. and 1:20 depending on the train. Fares were €7.35 each way.

If you start at the Basilica of San Vitale, you can by a €9.50 entry ticket for the five major sites. Great, comfortable little city. If you have Rick's guidebook, visit the sites first and then fill in the rest of the city walk in the book or you will be doubling back over much of the route

Ravenna, hands down!