Personally I would always opt for set dining rather than fredom dining. Having done 5 cruises, 4 of which offered freedom dining, we heard complaints on each ship regarding the process required for freedom dining - it isn't quite as free as it sounds as on some ships you have to book a table & time the day before or, even queue up each morning to do this. I would check the rules carefully before opting for this.
The menu is the same. The restaurants are identical, one on one deck and one below and each has their own kitchen.