We've been on all with the exception of the Horizon and love the Conquest - definitely one of our favorites. Having said that we have been on the Breeze once and found it to be ok (but it was during a time when we weren't feeling the best so that could have had some bearing on our view). We are going back on it in January for a Journeys cruise as we feel we need a redo on that ship. I would personally pick the side by side option as I would like to experience the Horizon and like I mentioned the Conquest is one of our favorites.
Regardless of which you choose I hope you have a fantastic time!!