I think all parts of speech are equally important for each part plays a vital role in spoken and written sentences.
Noun: honest, decision, cat, mountains
Pronoun: it, he, they, I, you
Verb: coming, jump, walked, was, is, were
Adjective: gloomy, dull, beautiful, tall
Adverb: very, honestly, beautifully
Conjunction: and, yet, for
Preposition: over, on, it, in
Interjection: whoops! Wow! Ick!