They each offer a great product. RCCL has more "glitz", Carnival has more of a laid back atomosphere, Princess, to me, has a more elegant atmosphere. Not "snobby", just a bit more elegant. One of the best differences is the muster. Princess has it right. You go to a lounge or the internet cafe for your muster station. You're inside, usually seated, not having to stand in line while everyone makes there way out to the lifeboats. You listen to the instructions, then at the end put on your life jacket, then you are dismissed. It is a procedure that takes 20 minutes-tops. You don't have 3000 people crowding into 1 door, it's great! For my taste, the food is better. I also think their shows are better. This is all my opinion, only. But each ship that I step foot on, I don't compare to another. Each ship and crew have their own experience. Some I enjoy more than others. It really doesn't make one better than the other, it's just that I enjoy Princess the best. It feels like "home" when I step on board. I prefer the Sun class ships to the Grand class, but that's my preference. The Grand class ships have a lot more to offer as far as ammenities.
I haven't done the balcony dining, but have heard some very good comments from those that have. It sounds like a wonderful idea for your anniversary, very romantic! We have used room service and they have been extremely fast, courteous, and brought what we ordered
I don't have any pictures of the Crown, but I'm sure there have to be some posted on Webshots, Youtube, or one of the other gallery websites. I bet if you google Crown Princess Pictures you'll find a bunch.