If I booked 2 adults today for September 21 or 22 7 night sailing (kids in school, not Fall Break so off-peak) includes port fees, taxes but not gratuities:
DCL Fantasy Deck 7 Aft Verandah 3893.04
Carnival Breeze Deck 7 aft Balcony 1945.54
RCCL Harmony of the Seas Deck 6 Aft Oceanview Balcony 2453.66
NCL Breakaway Deck 8 Aft Balcony 2677.44
There is a considerable price difference even over Royal and NCL.
RCCL is getting expensive as well. We are doing Regal Princess (7-night Eastern) over Thanksgiving in an interior cabin for 3 (which is currently sold out, so I'll use our price). Here are Thanksgiving week cruises:
Regal Princess: $2,086.80 + $300 OBC
Allure of the Seas: $3,808.07 (no OBC)
Oasis of the Seas: $4,516.13 (no OBC)
Harmony of the Seas: $4,742.60 (no OBC)
Disney Fantasy: $6,439.00 (no OBC) (NOTE: $5,834.79 + $200 OBC if you had OBB)
Carnival Breeze: $2,173.56 (NOTE: This is an Oceanview using the "More Equals Merrier")
My thoughts. The Princess is a wonderful deal that we got. Oasis and Harmony are closer to Fantasy prices, especially if you had OBB credit. You would have to determine if the difference is "worth it" to you. (For us, since we have a lot of OBB, we'd choose the Fantasy over either the Harmony or Oasis, the Allure would make me think). However, if you are going by value, the Breeze is a much better value than any of the others.
However, if money is no object, I'm picking DCL every time! Since money is an object, unfortunately, we'll go with Plan B on the Regal Princess and still have a great time!
Now, all this being said, why is Disney more expensive? Because they can get it from the market. So, apparently, the difference is enough for a number of people. However, the great thing about cruises is that all of these ships will be full and they will all be great experiences. One doesn't have to be "Good" or "Bad"...