Top five in what respects? If I had to pick the single greatest composer it would be J.S. Bach, but, in terms of influence on other composers, one could argue his son C.P.E. Bach was more influential (pioneer in early classical form) with dad sort of stuck in the baroque. I don't think Brahms was that influential either as a neoclassicist in the romantic period.
For personal favorites, Schubert would easily be in the top five. I would hate to have to choose between the likes of Haydn, Shostakovich, Stravinsky, Schoenberg, Verdi, Puccini, Tchaikovsky, Brahms, etc. for position outside of my top four: Bach, Beethoven, Mozart and Schubert.
