Ok, since the cat is out of the bag, I'll ruin the trick...
NONE of the pizza is really that great and doesn't compare to a good local spot (I know I live in SC, but we have some AMAZING pizza places cuz you yankees come retire down here when ur too old to shovel snow anymore

I joke...somewhat).
The pizza is good because of the experiences associated with it. Carnival keeps their pizza bar open 24/7 and most of us who've experienced it know that there are some hilarious things that go down while chomping a slice of pizza.
Heres a quick comparison:
Carnivals Dough- Sweet and thick (some liken it to Oprah)
Royal's Dough- More Traditional & Usually a little thinner and crisper
Carnival's Sauce- Usually little of it, but it's a sweeter tomato
Royal's Sauce- MINUTE amounts and a little bit saltier than CCL's
Carnival's Cheese- Usually browned over depending on who cooks & traditional white
RCI's Cheese- Idk what kind of cheese they use but it turns to plastic quickly
Carnival's Toppings- CCL does italian named pizza's Margherita, Napolitana etc. But they have 4-5 different kinds. They also have salads & calzones.
Royal's Toppings- They usually just stick to Cheese & pepperoni...though some ships put other random things on at times. Most ships don't offer anything with the pizza unless it's on a voyager/freedom ship then it's either part of or close to the Proménade Café.