We booked a cat R on the Wonder for my sister and I and our three kids (12 yo boy, 12 yo girl, and 16 yo girl). I guess we're a little unique because of our family situation. I want to be in the same cabin as my sister and as my son. And the same with my sister and her girls. At the same time, we don't want to be on top of each other either. And, we want enough bathrooms so that 4 women can get ready at the same time. That pops us up to at the very least a 1 BR suite.
I chose the R over the 1 or 2BR because we feel that its important that none of our kids feel like they're in steerage by having to sleep on the sofa. Perhaps that would be a different story if we were sailing as a cohesive family with all the money coming out of the same pot instead of a 'blended' one: "What? Why does my kid have to sleep on the sofa? Do I get to pay less then?" The increased expense of the cabin can save a lot of family grief.
Plus, unlike a whole hoard of people who only use their room to sleep and take a shower, I'm a 'hang around in the hotel room reading a book and looking at the view' kinda person. We're sailing to Alaska, so there will be a lot of view sailing by -- and I can open the curtains and look at it without someone yelling at me (since there's a living room with no one sleeping in it)!