Bach, Bach and Bach!
My passion lies witihin everything from Baroque (Albinoni, Corelli, Frescobaldi, Händel, Purcell, Telemann etc.) to Avantgarde, Impressionism and Minimalism, but no one has, and no one ever will, top Johann Sebastian Bach!
If I was to choose a era, it would probably be the Romantic era: Beethoven, Bizet, Brahms, Bruch, Chopin, Debussy, Dvořák, Gounod, Grieg, Liszt, Mahler, Mendelssohn, Mussorgsky, Offenbach, Puccini, Rachmaninoff, Rimsky-Korsakov, Rossini, Saint-Saëns, Schubert, Schumann, Strauss I & II, Tchaikovsky, Verdi, Wagner and many more, are all some of my absolute favorite composers of all-time!
As for contemporary music, there's only one man who tops them all...
... Michael Nyman!