the prettiest
Neither. Pretty is the positive degree. The comparative is prettier; the superlative is prettiest.
For the adjective "pretty" -- prettier is the comparative, and prettiest is the superlative.
prettier, prettiest
prettier, prettiest
prettier, prettiest
Prettier
prettier, prettiest
prettier, prettiest
prettiest, prettier
prettier, prettiest
prettier, prettiest
word comparative superlative pretty prettier prettiest hungry hungrier hungriest sad sadder saddest