The first movement is pretty much the best example of my model for composing, not even so much harmonically and melodically, but in the way Mozart builds the piece. It is built around my idea of "organic development". Each melodic phrase in a section is developed from the previous one in some way, but no repetition is the same; this creates a very strong impression of unity and direction upon the listener while ensuring the music doesn't become boring. To me it also has the feel of a through-composed piece (that the composer sat down one day and just wrote out intuitively, without stopping). I like that.
One of my favorite JS Bach organ pieces, especially for this time of year (I played this at church last Sunday, though not nearly as well):
A cry of defiance, and not of fear,
A voice in the darkness, a knock at the door, and a word that shall echo for evermore!
For, borne on the night-wind of the Past, through all our history, to the last,
In the hour of darkness and peril and need, the people will waken and listen to hear
-- Henry Wadsworth Longfellow