My wife and I cruised on the Liberty this past June for her birthday. This was our eighth cruise and fourth on Carnival, Princess being three and Royal Caribbean one. Of all our cruises this one was the best, the ship was beautiful, and the food was excellant. We were on the Verandah deck (cabin 8315), which is about midship, just below the pool on the Lido deck.
The only thing was because of the cabin location, you could hear them moving the deck chairs about 2:00 am which really wasn't a problem. Also we thought the balcony was smaller than most ships.
But no matter which one you decide on you will have a great time.