One of well established movie portals Taste of Cinema have just published the 25 Greatest Film Composers in Cinema History. According to the portal, Ilayaraja made into the top 10 of the list and was featured at number 9 while Hans Zimmer one of the world's most popular music composer was ranked at number 13.
Ilaiyaraaja has worked as a composer for more than 950 films and has composed over 4500 songs in Tamil, Telugu, Malayalam, Kannada, Hindi and English. The website has mentioned that "the maestro is particularly acclaimed for background score and his songs and background score played a very crucial role in the success of many films".
Source* - http://www.tasteofcinema.com/2014/the-25-greatest-film-composers-in-cinema-history/2/