Mahler... what can I say about Mahler? What is there to say that could truly do his genius justice? His symphonies are sublime, to say the very least! As for the 9th, it's an excellent piece, but certainly not my favorite of his. The 1st is a masterpiece, and probably the one that I listen to the most, but I'd say that the 2nd is probably my favorite, mainly because of its ending, which never fails to move me to tears.
And then... there's the 8th.
I would go as far as to say that the 8th symphony (also known as the "Symphony of a Thousand") is the greatest piece of music ever written. Though it's rarely performed with 1000+ performers, it is still an amazing experience to see/hear live, I'm sure. The end, which depicts the soul's acension into Heaven, is probably one of the greatest musical moments throughout all history... listen to it here -
http://www.johncareycompositions.com/reque...hler8ending.mp3
As you see, I'm an avid Mahler fan!