For the adjective "pretty" -- prettier is the comparative, and prettiest is the superlative.
prettier
Prettier the prettiest
Perhaps you mean the comparative form: the comparative form of the adjective pretty is prettier. (The superlative form is prettiest, but comparative sounds more like cumulative.)
prettiest
prettier, prettiest
prettier, prettiest
prettier, prettiest
Neither. Pretty is the positive degree. The comparative is prettier; the superlative is prettiest.
prettier, prettiest
Cute, beautiful, gorgeous
prettier, prettiest