You use prettier when you're comparing two people or thing.
ex. My mom is prettier than her mom.
You use prettiest when your comparing one thing to a lot of things.
ex. she is the prettiest of the three Thompson sisters.
Neither. Pretty is the positive degree. The comparative is prettier; the superlative is prettiest.
Prettiest
prettiest
"There is no one who is prettier than my mom!"
(Apex) Rosewood is the prettiest town in the state of Colorado.
For the adjective "pretty" -- prettier is the comparative, and prettiest is the superlative.
Neither. Pretty is the positive degree. The comparative is prettier; the superlative is prettiest.
Prettier the prettiest
the prettiest
prettier prettiest
prettier, prettiest
easy prettier or prettiest
prettier, prettiest
prettier, prettiest
prettier, prettiest
prettiest, prettier
prettier, prettiest