I have not yet cruised Carnival so I can't give you a comparison. But I have been cruising Princess since 1974 so you could say I am a "satisfied customer".
The Grand Class ships (Golden Princess is one of three sisters) are magnificent; lots or restaurants, lounges, fresh water pools; lots of deck space; lots of quiet areas inside and out.
The ships are kept in excellent repair and immaculately clean.
The staff and crew are friendly and courteous. And the food and service are excellent. The decor and ambiance is classy, even elegant--but not stuffy; lots of art and fresh flowers.
And Princess pioneered Alaska cruising almost 50 years ago and they really have it down. And I have always felt that Princess gives you good value for your cruise dollar.
I'm sure you would be very pleased with a cruise to Alaska on Golden Princess. If I can help in any other way, please ask.
Have fun deciding--enjoy the process.