I was a loyal Celebrity cruiser until 2019 when I tried Princess for an Iceland and Norway cruise. At that time, I would have said Celebrity had much better food, but not any more. Princess has improved a lot and my last three cruises on Celebrity had very unimpressive meals.
I think that the cabins on the Summit are fine but nothing special although I always liked the Sweet 16 balconies. On the Sapphire Princess, the extra-deep, half-covered balconies on Caribe deck are my favorite. They are twice the size of other balconies.
Celebity’s big advantage for me is the non-smoking casino. For a short cruise it won’t be much of an issue but Princess has self-service laundry and very large closets that are a huge advantage on longer trips or if you’re bringing a lot of sports equipment like golf clubs or scuba gear.
In general, I think Celebrity and Princess are more alike than different. Were Elite on both lines and I base my decision on itinerary first, then cabin availability and total cost including drinks, gratuities and internet.