While it is true that this cruise is free, since you did not like the Miracle...I am not sure you will like the Victory.
We cruised on the Miracle just a few months after you and it was one of our best Carnival cruises. (I think we had done between 15-20 at that time.)
The Victory will be consistant with the food, entertainment, experience and service as the Miracle...just a different lay out.
If you are thinking about sailing out of San Juan, I would only sail when school is in session. But that is because we only sail (from any port) when school is in session. We find it a better experience.
My 18 year old son and I have 34 Carnival cruises under our belts (on all but 3 of the ships)in the past 12 years. Some were better than others, but only one (on the Holiday in Dec 2007) has ever been below par.
Since it is free....I would go on the ship that provided the best ports....but do remember that going to a port is not guaranteed. (weather, medical emergencies etc can cause a port to be skipped)
If you go with the right frame of mind, you will have a good time. If you go thinking it will be bad, but you are going because it is free....you are wasting your time...free or not.