quietest dishwasher - GADGET
0 Since quiet is a two-syllable adjetive, the rule-of-thumb would make more quiet and most quiet the expected comparative forms; however, quietest and quieter are six-times more common (or, as many would say, "commoner." Both forms are correct, but the single-word construction is what the American ear expects to hear. Assume there is original source text: This restaurant is amazing with "delicious lasagna" and great service. Make sure you go 6-7pm for the quietest times.
Context Explanation
I want to quote "delicious lasagna" b... The quietest-singing bird Highest-grossing film isn't an idiom, but simply a superlative compounded with a present participle being used as an adjective, and is therefore hyphenated.