La Gazza Ladra by Rossini is my favorite piece of clasical music so he gets my vote. his overtures for Guillaume Tell and Il Barbiere Di Siviglia rock as well :H
It's really hard to choose just one! But composers who I particuarly love include Mendelssohn, Chopin and Beethoven.
Depends on my preference of the moment. Usually Beethoven, Bach, Mozart, Franz Joseph Hayden. Generally speaking, if they're German and dead, then I'll probably listen to them. Guess I'm a little wierd like that.
Depends on the era and my mood. Excluding post-WWII composers, J.S. Bach, Chopin, Bartok and Debussy are probably my favorites.