My experiences are pre-covid. I found the NCL entertainment better than carnival, with the exception of comedy shows which Carnival excels at.
I liked the dining room food on ncl better than carnival, but the carnival's buffet better where you can always get a deli sandwich freshly made. Better comfort food in general. O'Sheehan's on ncl is a big plus, pub food available day and night (never tried late night),
Ncl has nothing comparable to a ship on a stick... but no one in a pirate costume will impose on your dinner either.
Carnival gets a younger partying crowd which, to me, translates to some serious people watching opportunities. Overall NCL is a little quieter and likely to have more bells and whistles.