What are your top three favorite classical compositions?

Vivaldi The Four Seasons

Beethoven 5th Symphony 

Handel Messiah 

Schubert Symphony 9 

Beethoven Violin Sonata No. 5

Mahler Symphony 9

As it appears most folks like orchestral, a few that are heard more often in my house - Sibelius Sym #4 (and his Finlandia Hymn, original version, by male choir, highly recommended for those who feast on nationalistic music), Last movement of Mahler's #2, all of Mahler #6, Prokofiev's Piano Concerto #3.

Another three off the bottom of my head --

Mahler's Wunderhorn songs.

Stravinsky's Petrushka

Puccini's Turandot.

A great question.  For right now, I'd have to say:

--Beethoven's Ninth Symphony.

--Mahler's Second (Resurrection) Symphony

--Mozart's Don Giovanni