Saint-Saëns' 3rd with the power of the king of instruments, the organ, complemented by two pianos and full orchestra is to me the top of the range.
my favorite symphony

Not in any particular order........ Mahler's Third, Schubert's Eighth (the "Unfinished"), Beethoven's Third, Haydn's any-of-them (he wrote 104), Brahms's 1st and 2nd, Mozart's 35th, Tchaikovsky's Sixth, Saint-Saens's Third, Dvorak's Fifth (the "New World"). I know when I'm falling asleep tonight I'll be kicking myself for not thinking of a number of other favorites, but I can safely say the above are among my top favorites.

Beethoven 5,9,7,6 :)
Mozart 40,25,41
Too bad bach did'nt have symphonies yet anyways, brandenburg concertos are all good

Beethovan's 6th...and though not symphonies, I would have to add Tchaikovsky's 1812 Overture and Bach's Brandenburg concertos.
I am agreed with akapovsky regarding Beethoven's Symphonies. I appreciate the Fifth for its dynamism, the Sixth for its depiction of the pastoral and country life, and the Ninth for simply being the epic, glorious finale to the Symphonic Suite, as if it were a celebration of humanity itself.

Sibelius - Symphony No. 7
Honorable Mentions:
Mahler - Symphony No. 10
Beethoven - Symphony No. 7
Schumann - Symphony No. 1, "Spring"
Sibelius - Symphony No. 4 in A Minor
Shostakovich - Symphony No. 8
Mahler - Symphony No. 3
Berlioz - Harold in Italie
Hindemith - Symphonia Serena
Vaughan-Williams - Symphony No. 5
Copland - Symphony No. 3
Bartok - Concerto for Orchesta (technically, not a symphony, but symphonic...)
hello classical music fan .. i wanted to share with you my favorite symphony and classical music piece ..
its symphony no.2 for Rachmaninov
and here's the 1st movement in it ..
http://www.youtube.com/watch?v=W21USUhx7Bw
i hope you like it ..