Hi heavenlyescapes, and welcome to cruise-chat.
I've sailed on both Carnival and HAL. I enjoyed both, yet HAL was definitely a notch above in food quality (subjective, of course), food presentation, and service. I'd give Carnival the edge in entertainment. But a lot also depends upon the ship you're sailing. I like the intimacy of the smaller HAL ships (~55K tons, 1300 pax), and have not been on one of their larger, Vista class ships.
One big difference between the two lines -- and this is a recent move -- is that HAL now offers pax a choice between an anytime dining option and fixed seatings for the duration of the cruise.