My first and only cruise with Princess was because it was cheaper than Carnival. I like Princess, they run a good cruise. They had a lot of venues before and after dinner that had live music where you could sit and enjoy a drink and relax. I didn't notice a difference in food, service, staff or entertainment.
I have been on a lot of Carnival cruises and every ship and sailing is somewhat different than the other, sometimes good sometimes bad, but never enough to ruin my cruise.