If you have enjoyed your cruises with these other lines, there is no reason to think that you would not enjoy Princess. Each line has its own cheerleading section, but the when viewed from 50,000, they are more alike than similar. The biggest difference is when you add the Oasis Class ships into the equation. A ship that hosts 5,400 people simply cannot be compared to anything that Princess offers. Those floating cities are a "love it or hate it" proposition in my opinion. For me, those ships are the destination and the vacation, and the port stops are secondary. There is nothing that I enjoy about an embarkation, disembarkation or port off-load procedure that involves 5,400 people. That number can swallow a port alive and overrun its services and offerings. But take those ships out and all four lines that you mention are similar in overall texture.
Specifically, what keeps me coming back to Princess is:
User-friendly booking on the website. It is astonishing how other cruise lines make picking a cabin so complicated.
MDR and buffet food are more than fine, and the Specialty Restaurant upcharge is reasonable. No cruise line should charge $50+ per person above the already-paid fare.
Generous wine allowance. I like to enjoy the best bottles from my cellar when I am on vacation as I have the time to sip, enjoy, reminisce, and geek out. Bottles that are saved for "special occasions" are typically consumed while on vacation, because that IS my special occasion. Princess has these other cruise lines beat by a mile with its unlimited bottles/corkage fee policy.
The overall approach that the destinations you are traveling to are the real focus of your cruise without a lot of unwanted (by me) distractions where the cruise line tries to make you believe that being on the ship is the most important part of the vacation. Of course, the time on board is very enjoyable. But the real purpose of the cruise is to participate in world travel, not childish games.
Again, I am not accusing all of these other cruise lines of failing in all of these things. But when I put the whole bundle together, Princess fits us a bit better than these others.