J, you are going to have to compare apples to apples. For Princess, at least a minisuite would be required. For Pacific Princess, you have to go to the cabin at least equivalent to Penthouse on Oceania's version of that ship.
Then, does quality of service and food matter? If all you believe is that "I didn't have to cook it" then McDonalds will work.
If the extras that Mariner provides (all inclusive, room, service, food) don't make up for the extra cost; then you might as well choose Princess.
