Well, I know that there are different styles for different ships. Carnival is known for being very loud and full of young people. They're known as "Carnivore" in the cruise business. Disney is clearly for people with young kids.
That's what I know about Cruises from reading David Foster Wallace's "A Supposedly Fun Thing I'll Never Do Again."
You should first decide what you want and then figure out which cruise line is the best fit. I think, generally, the mid-size ships are the most comfortable (less feeling like cattle). But if you're a teenager, you'll have trouble meeting people your age, so you might want to petition yr parents for something larger. Maybe even Carnivore.