Well first off I need to have an idea of the ports. So I looked.
Jewel Of the Seas 13 day:
Kings Wharf, Bermuda;
Brussels/Brugge (Zeebrugge), Belgium;
Harwich (London), England
Crown Princess 14 day:
Ft. Lauderdale, Florida
Marseille (Provence), France
Florence/Pisa (Livorno), Italy
Rome (Civitavecchia), Italy
I have been to Lisbon and it's really nice. Also the Jewel of the seas does stop in Bermuda before the crossing, which would be interesting.
However, with the crown princess you see more of Spain and Italy. In 2008 we took a cruise the ended in Civitavecchia (about an hour from Rome). After the cruise we stayed two more days then took a Eurostar train (4-5 hours) across the Italian countryside to Venice and stayed in Venice. I loved Venice.
If the price is the same I would book Crown Princess to see more of Europe than take the train over to Venice. The train ride was comfortable and inexpensive. Here is the website for the Italian train system. http://www.trenitalia.com/cms/v/inde...0080a3e90aRCRD
The train station in Rome is Termini and Venice the station is St. Lucia. Our Cruise was April 26 to May 10 and our ports did include Livorno (great place to shoe shop) and Rome plus we stopped in Malaga, Spain. So the weather at this time of year was sunny and in the 70s. It was a perfect time to see Venice I have heard in September Venice has some flooding. Here are some pictures:
Pisa (near Livorno)
Spanish Steps in Rome.