Raja stormed in, when there was a vacuum and not much of innovation in the tamil film music industry and slowly when people began listening to hindi songs. With his style of folk music he grew with and WCM he learnt in later days, he swayed his magical wand and whole of tamil nadu were mesmerised with his musical magic. His songs gained popularity solely through Srilankan radio, AIR and Doordarshan's "Oliyum Oliyum", which according to me is a great feat comparing the number of times each song is played in satellite channels. No music director would have enjoyed the monopoly that Raja had in TFM for more than 12 years. With all his experimentations in all genres, he had undoubtedly proved his calibre.
When Raja was in his peak, continously churning out hits after hits, no one would have even believed that a whizkid would make a thundering entry and steal away millions of hearts. Apart from his soul-stirring tunes, Rahman introduced global sounds in his songs with crystal clear audio quality. Most of his albums received negative reviews on first hear and his songs usually have growing effect and once they grow into the listener, they never wear off. With the advent of satellite televisions and countdown shows telecasting new songs all the time, his songs easily invaded the people's hearts. Rahman never turned back after that and with Rangeela songs being a rage in Bollywood, he gave nightmares to Anu Maliks there. From Bollywood as launch pad he has reached the Global market of music and is now an Universal Celebrity.
We must be proud to have these extraordinary geniuses from our land. It is quite normal for a person who has grown up listening to tunes of Raja, to find it difficult to accept Rahman's innovations. But on the contrary, Rahman's fans who are mostly under the 30+age group, digging on Raja's music and underrating his compositions, is not fair at all. Those people should understand that it would take most of their considerable time to judge Raja after listening to thousands of the songs he has composed for the 800+ films so far, not leaving any styles or genres upturned.
So, let's put away all the arguments and discussions about trying to find answers for "Who's the best, Raja or Rahman?" and let their magical music compositions do the talking. We'll just listen to their music and enjoy.