I went with the guarantee myself. Since they promise you a room of at least what you paid for what have you to lose. I paid for a room at the lowest level and price and was pleasently surprised to find out we were upgraded 4 floors at no extra charge. The only way you can lose is if when you book you have a choice of a room at a certain part of the floor you like (say the middle or front or back) and later you find yourself assigned a different part. Like I said we went from the lowest level to one of the highest level which would have cost me about $400 more up front. My travel rep told me that Carnival will upgrade early bookers who choose guarantee to unsold better cabins, then sell the lower cabins to the last minute bargain hunters.