Just concluded our Dec 11, 7 day cruise and since it was only our 2nd cruise my basis of comparison is a previous 5 day RCL cruise.
I believe that Carnival is a good option if you are on a budget. Our biggest let down was the food, it was OK, and the service ranged from poor to very good. 2 nights out of seven it took us almost 2 hours to get through dinner in the Truffles restaurant (especially where Edgar was the head waiter). One night they failed to refill our water glasses! I also did not care for the arrangement of the buffet area (Unicorn restaurant). Unless you are set on one of the several stations they have (grill, chopsticks, etc.) you will need to check all of them out by walking most of the entire restaurant to make a choice.
We were not big on the activity side; we took in several of the main shows and found them enjoyable. We also went to the comedy club and saw a couple of shows and found them enjoyable as well. My wife and two daughters (adults) also enjoyed the Serenity adult's only area (when you could find room). We had and 11:00 flight so we used the 'self assist' option and had no problem getting to the airport.
Since we had to purchase 3 staterooms for our family, we choose to go with minimal extras for our rooms (inside staterooms). We were all on deck 7 and all rooms were adequate. Service was very good, no complaints from our family.