The important thing is the itinerary. If it's a first Alaska cruise, a call at Glacier Bay is essential.
Celebrity has excellent kids' programs. There were 250 of them on Horizon last week and they were almost invisible.
I've never heard of the five (or any) hours of quiet pool time after 13 Celeb cruises. Pools close at a certain hour and re-open the next day.
Dress on Alaska cruises is far less dressy than on some other itineraries, except for formal nights. Even then, ladies tend not to go the "gown" route in favor of quiet silks with interesting jewelry.
An Alaska cruise is port-intensive, so there's not nearly the need for things to keep the kids occupied as there would be on a cruise with a lot of at-sea days.
You might want to consider a walkie-talkie system to keep tabs on the kids.
My vote goes to Celebrity.
pamda -- CM First-Time Cruisers Editor