Its really hard to compare line to line, each one is different, diverse offering something for everyone,kind of like comparing apples to oranges.
Making a broad-based comparison, IMO i would put Princess squarely in the middle, above NCL and just below Celebrity.
What we like about Celebrity is the up-scale clientele for a mass-market line, the food and service is quite good. My husband prefers set seatings, although the rest of us like some variety. Doing totally free-style though was not for us. The activities are less varied on Celebrity, and this year's itineraries to the Caribbean for 7 days are quite poor. We are 2 families traveling together with 2 teen-age boys.
I posted on your other thread before I read this one!
I don't know exactly what you mean by "up-scale clientele"? On any cruise out of Galveston there will be a lot of us "laid back" Southerners .
I believe that you can reserve a table for a certain time each night if you want to avoid Anytime Dining. We never did that, so I'm not sure how it works.
There are many activities on the Grand Princess, and I don't think the two boys will have any trouble finding things to do and making new friends.
We found the staff to be very nice and helpful, but they are probably not as "formal" as the staff you had on Celebrity.
Personally, we considered a Celebrity cruise, but decided that it was too up-scale for our tastes .
"A truly happy person is one who can enjoy the scenery on a detour."
Without a doubt for me - Princess first, Celebrity a close second and NCL (not for me cuz only have Free Style Dining and I like Traditional). Pluses for Princess - choice of dining - Traditional or Personal Choice where you can make your reservation each night; Celebrity Traditional only.
Princess fresh water pools (only cruise line that has them) - the rest are salt water.
Princess actual refridgerators which keep drinks and ice cold - Celebrity = mini bars (think, but not sure the same for NCL).
Food - equally good on Princess and Celebrity (been quite a few years since I took NCL) as is the dining room and cabin service.
I cruise the Emerald Princess, Eastern Caribbean on April 16, 2012