I've cruised both Princess and Celebrity in Europe...and my choice, hands down, is the Millennium...largely because of the cruise line itself--I find Celebrity to be superior in just about every way imaginable in terms of food, service, entertainment, etc....secondly, for the ship...The Millennium is just far superior in terms of passenger-to-gross tonnage ratio and passenger -to-crew ratio...
Let's also take a look at the all important itinerary:
Grand Princess:
1Barcelona, Spain 10:00 PM
2Marseilles, France 8:30 AM--6:00 PM
3Florence/Pisa (Livorno), Italy 7:00 AM--7:00 PM
4Rome (Civitavecchia), Italy 7:00 AM--7:00 PM
5Naples/Capri, Italy 7:00 AM--7:00 PM
6At Sea
7Mykonos, Greece 7:00 AM--2:00 PM
8Istanbul, Turkey 8:00 AM--6:00 PM
9Kusadasi (for Ephesus), Turkey 12:00 PM--7:00 PM
10Athens (Piraeus), Greece 6:00 AM--5:45 PM
11At Sea
12Venice, Italy 12:30 PM
13Venice, Italy 5:00 AM
Millennium:
Wed barcelona, spain -- 7:00 PM
Thu villefranche (nice), france 10:00 AM 11:00 PM
Fri livorno(florence/pisa),italy 7:00 AM 7:00 PM
Sat civitavecchia (rome), italy 7:00 AM 7:00 PM
Sun naples, italy 7:00 AM 7:00 PM
Mon at sea -- --
Tue mykonos, greece 1:00 PM 11:59 PM
Wed santorini, greece 7:00 AM 11:15 PM
Thu piraeus (athens), greece 7:00 AM 11:00 PM
Fri at sea -- --
Sat dubrovnik, croatia 7:00 AM 5:00 PM
Sun venice, italy 12:00 PM --
Mon venice, italy --
Both itineraries are virtually the same in terms of Barcelona, Livorno, Rome, Naples and Venice...
Here are the trade-offs on the other ports:
Both ships visit Mykonos and Athens...But, Princess gives you only the morning in Mykonos while Celebrity gives you the afternoon (prime beach time) and the evening until midnight--so you can explore the nightlife on the island...
In Athens, Princess gives you a full day...until 5:45...but Celebrity again gives you the chance to go out and enjoy the nightlife...
In the south of France, Princess gives you a day in Marseilles (which is a big, dirty port city...but allows you to do excursions in Provence) returning to the ship before 6... while Celebrity puts you on the Riviera in Villefranche--right next to Nice and Cannes and a short ride into Monte Carlo--and allows you until 11:00 at night...
The major itinerary differences are with Istanbul and Kusadasi on Princess versus Santorini and Dubrovnik on Celebrity...On Princess, you get an 8-6 day in Istanbul and an afternoon in Kusadasi...With Celebrity, you get a full day in Dubrovnik and a day and night--until 11:15 in Santorini...
As far as those ports go, it is personal preference whether you'd prefer Istanbul and Kusadasi or Santorini and Dubrovnik--all four have their charms, historical and archaeological wonders and other benefits...
But, clearly, Celebrity gives you more time in port...
All in all though, one thing is true...You can't go wrong either way...and BOTH of these itineraries give you the opportunity to do distinct pre- and post-cruise stays in Venice and Barcelona--neither opportunity of which is to be missed..