Carnival is a middle of the road cruise line. I have been on 5 Carnival cruises all through the Caribbean. With a family of 4 and kids in the ages that can still enjoy Carnival's kid's programs it is an easy decision. There's not much glitz and glamor with Carnival and they are designed around cruisers in their 20's and 30's (in my opinion). We have been on a few excursions of which half of them ended up being a terrible experience. Carnival was good about handling the complaint regarding the excursion.
For the price, Carnival is a reasonable choice.