Troilus and Criseyde and Book of the Duchess come in a close second, with Spenser's Amoretti sonnet sequence a close third. Oh! and Goethe's Faust Part I is a heart-wrenching 1.5 in there somewhere, the second greatest ever written. Here's a tad from one of the earliest stanzas of Epithalamion.

Bid her awake therefore and soone her dight,
For lo the wished day is come at last,
That shall for al the paynes and sorrowes past,
Pay to her vsury of long delight,
And whylest she doth her dight,
Doe ye to her of ioy and solace sing,
That all the woods may answer, and your eccho ring.

What I love about Epithalamion is the way Spenser twines the meter in with the stanza-end repetition and the final envoy; they seem to pulse, almost like a heartbeat, his heart beating for his beloved. The mastery of language is sublime. There is not a false note in any syllable of any word, any beat of any line. Reading it at leisure in a quiet room is almost transcendental.

And Goethe's Faust! The tears one sheds over Gretchen in the dungeon, over Faust's anguish and his fury at Mephistopheles' deception. The rage one feels at Mephistopheles' cold-hearted indifference and callousness!

[Then of course, with streaming eyes and beating heart, you quickly turn the pages to Part II, scene i, and say ...: "What!!??" Turning back pages, you say, "Did I miss something?? Surely this can't be what's next!?!?!" But surely it is. Then you are challenged to see the greatness in Faust Part II written long, long after Goethe renounced Romanticism (of his own creation) and embraced Classicalism. Part II, now that I've mastered appreciating it, is number four on my Favorite and Greatest List.]

Here's a tad from Part I when Faust discovers Gretchen is in the executioner's dungeon awaiting hanging after Mephistopheles' deception:

FAUST
Cease thus to gnash thy ravenous fangs at me! I loathe thee!--Great and glorious spirit [apostrophe to the macrocosm], thou who didst [once] vouchsafe to reveal thyself unto me, thou who dost know my very heart and soul, why hast thou linked me with this base associate [Mephisto], who feeds on mischief and revels in destruction?

MEPHISTOPHELES
Hast [thou] done?

FAUST
Save her!--or woe to thee! The direst of curses on thee for thousands of years!

MEPHISTOPHELES
I cannot loose the bands of the avenger, nor withdraw his bolts. "Save her!" Who was it plunged her into perdition? I or thou?
(FAUST looks wildly around.)

MEPHISTOPHELES
Would'st [thou] grasp the thunder? Well for you, poor mortals, that 'tis not yours to wield! To smite to atoms the being however innocent, who obstructs his path, such is the tyrant's fashion of relieving himself in difficulties!

FAUST
Convey me thither! She shall be free! (A Goomy Day. A Plain)

My favorite poet is a contemporary poet: Suji Kwock Kim. Ever since I read her book of poetry entitled "Notes from the Divided Country", I have been a big fan of her clear, intense and thoughtful writing. This book of poems was the winner of the 2002 Walt Whitman Award of the Academy of American Poets.

My favorite poem of hers is "Borderlands", which she wrote to honor her grandmother. It is a poem that shows the horrors of war and how her grandmother experienced the death of friends as she and they attempted to flee from Japanese soldiers and

...escape across the frozen Yalu, to Ch'ientao or Harbin.

One of my favorite lines in the poem is:

I saw men and women from our village blown to hieroglyphs of viscera,

     engraving nothing.

This poetry book was also a Griffin Poetry Prize nominee. Recently, Suji Kwock Kim won 1st Prize in the Gregory O'Donoghue International Poetry Competition for her poem "Sonogram Song."

There are so many to choose from!  I love Robert Frost, especially "Mending Wall," mostly because he is my dad's favorite poet.  However, personally I love Langston Hughes's poem "Dreams" because it always gives me goose bumps.  It is a romantic notion, to me, to hold onto dreams.

Hold fast to dreams
For if dreams die
Life is a broken-winged bird
That cannot fly.
Hold fast to dreams
For when dreams go
Life is a barren field
Frozen with snow.

I am also a big fan of the older poems, such as Spenser's "One Day I Wrote Her Name Upon the Strand" because it is so simple, and "The Tyger" and "The Lamb" by William Blake because I love the language, especially "fearful symmetry."

To me, a poem can speak to me over and over again.  I also like to discover knew ones though!

Just so you know, I am not committing to one favorite at this point:D I do love the work of William Carlos Williams. There is such intensity and depth in many of his poems, and yet his use of language is so simple. The poem "This is Just to Say" is a prime example. eNotes also has some great resources on this.

This is Just to Say

I have eaten
the plums
that were in
the icebox

and which
you were probably
saving
for breakfast

Forgive me
they were delicious
so sweet
and so cold

I love the poetry of Poe and Kipling and especially that of e e cummings. But I particularly enjoy the verse of the more obscure and still-living Greenwich Village poet Edward Field (1924 - ), who's interest in cinema led to a number of poems based on old monster movies (including many about Frankenstein and my favorite, Curse of the Cat-Woman).

If I have a favorite poet (as opposed to a series of favorite poems), it is A.E. Housman.  I fear that I like him as much as anything for the fact that his poems rhyme nicely and have a good rhythm to them.  However, I also like (or at least am affected by) his sense of aching sadness about the transitory nature of life.  Like him, I often think while I am doing something of how I will not always have the chance to do that thing.   (For example, when I hold one of my kids and feel the size of them and look at how they act, I feel a nostalgia for something that is not even in the past yet.)  Housman captures this in “Loveliest of trees, the cherry now”

Now, of my threescore years and ten,
Twenty will not come again,
And take from seventy springs a score,
It only leaves me fifty more.
And since to look at things in bloom
Fifty springs are little room,
About the woodlands I will go
To see the cherry hung with snow.