I understood that this was the whole point of the balancing stage of the appeals process to balance the prejudice to the school against the prejudice to the child of not being offered a place. I don't know how you can do this without reference to the alternative which has been offered.
The alternative school can of course be referenced, but it is the way it is done that is important.
E.g. 1: "Preferred School A has a strong history of supporting children with dyslexia, while Allocated School B has stated to us that they do not believe they have the facilities required to support our child." No problem with that at all.
E.g. 2: "Allocated School B is in a rough area (read: has rough kids ...), while Preferred School A is in a nicer area where our little flower will feel safer walking home." Ouch!
As a rule of thumb, you should always remember that a member of the panel might have a child or grandchild who has attended School B. Nothing you say should be capable of offending that person.