I have to go with Mozart, Beethoven, and Chopin myself.. My favorite piece is Beethoven's Moonlight Sonata. Not any of the movements in particular, just all three movements in one is a great piece of work. I have to say it's my best cause it's what I listen to at night when I can't sleep, and it gets the job done within the first movement..

Another I think would be Für Elise. Both great pieces of musical art.

Mozart I guess would be Symphony No.21 in A. Found a nice site for his music too by the way if anyone is interested. (http://www.mozart-weltweit.de/mozart00.htm)

And lastly, Chopin, 3 Nocturnes Op.9, A Madame Camille Pleyel. I don't know why but this one is the one i get stuck on when going through his list.