I have only cruised RCL and Celebrity and I prefer Celebrity.
Celebrity has the ambiance I like. No announcements, wonderful and consistent food, especially the dining room, very attentive service. Decor is subdued, all the niceties are there. All the passengers are also very courteous towards their fellow cabin mates. I take notice of that.
I have been on the Horizon, Summit, Constellation and Millenium, (Century booked for 2006 and Infinity booked for 2006) .
I do prefer the Summit, Constellation and the Millenium. The Horizon was nice, but it needs a facelift and was a little too bland in furnishings, but the service and food was a 10. Keep in mind I had just come off RCL's Brilliance of the Seas then went on the Horizon, so I was a little dissapointed.
But if you want to go to Bermuda, Celebrity is the ship to do on. Great itinerary.
This did not stop me from trying Celebrity again as you can see above, I love Celebrity.
Now for RCL, been on the Explorer of the Seas twice and the Brilliance and Majesty. I prefer the Radiance class which is the Brilliance. Wonderful ship, food not quite a 10, but the ships is a beauty. I'm booked on the Jewel on a back to back and am looking forward to it. I am going on the Voyager on a repo cruise, couldn't pass the great price.
So for the future, RCL's Radiance class and Celebrity's Millenium class are my favorites.