On the power of words:
* "Poetry is the universal language which the heart holds with nature and itself." - William Hazlitt
* "Poetry is the music of the soul." - Voltaire
* "Poetry is the expression of the imagination." - Percy Bysshe Shelley
On the beauty of language:
* "Poetry is the art of uniting pleasure with truth by means of beautiful language." - Samuel Taylor Coleridge
* "The best poems are those that make the reader think." - Robert Frost
* "Poetry is the art of making things seem more important than they are." - Oscar Wilde
On the essence of poetry:
* "Poetry is the spontaneous overflow of powerful feelings: it takes its origin from emotion recollected in tranquility." - William Wordsworth
* "Poetry is a deal of joy and pain and wonder, with a dash of the dictionary." - Khalil Gibran
* "Poetry is not a luxury. It is a necessity." - Maya Angelou
On the universality of poetry:
* "Poetry is a universal language which the heart holds with nature and itself." - William Hazlitt
* "Poetry is the universal language of mankind." - Henry Wadsworth Longfellow
* "Poetry is the language of the soul." - Rumi
Ultimately, the "best" quote depends on your personal taste and what you're looking for. I hope this list gives you a good starting point!