Pyotr Ilyich Tchaikovsky.  I was tempted to say Mahler, but Tchaikovsky wins on sheer range, he could write symphonies, ballets, overtures and operas fantastically.  Pieces like the Nutcracker Suite and the 1812 overture are sublime works, not to mention Piano Concerto number 1.  His work is so consistently amazing that I can't think of anyone more deserving of being the answer to this question.

There are so many pieces I could upload, but I've decided to go with two of those I listen to most often, conducted here by London Symphony Orchestra.