There are a lot of average lines and some really opulent ($$$$) but keep in mind they all sail the same beautiful water and end up at the same ports. So itinerary and price are my first factors. Research what you want and determine how much 25 folks want to spend. Most have kid programs but my the big thing ours enjoyed or missed depending on the ship was a real, big water slide.
Also, how old are your adults. Holland America is a pretty old crowd, Princess is younger and Carnival very young as is Norwegian. Disney is in the middle.
If money is no object I'd pick seaborne yacht club, if money is an object I'd shop princess first and then others.
The big variables are food and service. They've all cutback and it goes up/down. We always set our expectations for lousy food and lousy stewards knowing the ocean will be pretty and we won't starve. In all our many cruises they've all been pretty good to excellent with food and service. We have not had a bad cruise yet. But once you get a high mark on one ship you have to caution against something less disappointing you.
Vacationstogo.com is a good shopping place and you choose to book with them or cruise line direct. Usually same price.
Cruisetimetables.com is a great site to click on ports and see what boots will be where/when.
-------------------- Just the other night I was sleeping under a bridge and now here I am on the grandest ship in the world having champagne with you fine people.
Jack Dawson - Movie Titanic
Short answer: There is no such thing as the one, "best" cruise line.
As PelicanPirate points out, there are a lot of different criteria that you might apply, and so only you can decide which one is best for you. Give us some more details about what sort of experience you want, what your budget might be, what areas you are interested in, and then maybe we can offer some more useful suggestions.
Agreed. The OP needs to consult a cruise travel agent for advice. They know all the lines, they can advise you what is best, and get you a better deal, ESPECIALLY when you are talking about that number of people.