Hi lafayette, welcome to CruiseReviews! Congratulations on your upcoming cruise! The Allure is RCI's newest ship and is much larger than the Freedom. My best suggestion is to talk to a good travel agent, one that is CLIA certified. They can ask the questions that need to be answered to help insure a great cruise. The ships of today are so large, you barely notice movement. If you're worried, talk to your doctor before departing, they can prescribe patches or medicine to help you with your imbalance.
Either ship would offer something for everyone to enjoy. It would probably depend on the itinerary that bests suits your interests. Please let us know what you decide:)