Another vote for Royal Carribean....
We've done a few cruises we are leaving on Saturday for my 5th, and my husband's 6th, 3rd cruise for two of our kids and it will be the 1st for the baby. We have a 12 year old, a 3 year old, and an 18 month old.
We've done cruises on Voyager class ships twice and one of the smaller ships once and also once on Carnival but will never do Carnival again. For us, Voyager class ships are the way to go and I disagree that they are too crowded. There is much to do for all age groups.
When we were on our Carnival cruise, my 11 year old daughter was bored, even though she had a blast the year before on RC's Mariner. The food was not as good as what we had previously experienced on our RC vacations.
One thing that was better on Carnival, though, were the shows. They were really much more than you'd expect on a cruise ship but that's not enough to make me come back.
This is a small peeve of mine about Carnival but really annoyed me every day while on that vacation. I was pregnant at the time so I wasn't drinking any alcohol but I did want to sit with my husband in the bar areas (non smoking of course) while he enjoyed a cocktail ever once in awhile. Each time I wanted something other than water at one of the bar areas, I had to either pay for it or go upstairs to the buffet and get my own lemonade or tea. On Royal Carribean, certain drinks are complimentary anywhere on the ship, so I could enjoy a glass of lemonade with my husband at the bar anytime I wanted without having to pay for it. Being pregnant and wanting something to drink all the time, I found it so annoying to have to go all the way up to the top deck each time I wanted something to drink.
I know that is small, but it's just a sample of why Carnival falls short. There were so many small things that added up and made it a less than perfect vacation.