I have sailed on both these ships and greatly prefer the Miracle. I love the adult only pool that is aft on Lido deck. Also, their almost nightly comedies are a hoot.
The Star had smaller closets than the other grand class ships and it is one of my least favorite Princess ships.
The food on both lines are hit and miss as Princess has really gone downhill in their food dept. IMHO.
I don't think you can go wrong with either cruise, but I prefer the up beat and laid back passengers on Carnival. That itinerary always attracts an older crowd, but they are far less cranky on Carnival. IMHO
I've done this itinerary many, many times on both lines and now only do this itinerary on Carnival.
The Miracle has many, many live music choices every evening/afternoon. From violin playing, to pop, to slow melodic music. I love the bands in the Red Frog Pub at night.