Actually there is nothing called Favourite raga for MSV. He will create a song – it is for fans and knowledgeable ones to decode, decipher and find the contents – including raga or not, or deviated form of a raga etc…. i read somewhere once – one Mannar fan had written that, since it is not possible to find ragas etc of MSV songs, it is better to start a new series of ragas starting with Viswa – like VISWAMOHANAM, VISWAKALYANI etc…
Each MSV song is like a flowing river – you don’t know where it is going to turn next. He will probably start with some raga as inspiration and stick to its patterns. But, bringing the right emotion is the most important thing to him. So he will deviate (for example, use foreign notes) from the main raga he had in mind, as needed. So, at the end you can’t classify the song under a raga because of the deviations, but the raga feel will be there in the song. One can take a different approach which is – follow the rules of the raga’s notes properly, but end up in a composition that follows the rules but you don’t have the feel of the raga. Such is NOT MSV’s style.
Another big mystery with his songs is – Exactly what raga he had in mind for each song – nobody may know except him. Expert listeners can argue as much as they want. Take muththukkalo kaNgaL. Many call it as Madhyamavathi. But one music expert told in Jaya TV thEnkiNNam programme that the raga is a rare Hindustani called Megh Malhar. Someone may call it something else.
Once in a TV discussion, someone kept asking MSV what was the raga used in nAn pEsa ninaippadhellAm. MSV was very hesitant to say simply because he uses ragas only as inspiration, but deviates. After some prodding he said it is built around sivaranjani. If you actually see the notes of the song, you will see sivaranjani mostly, but ma1 coming often, which sivaranjani doesn’t allow. That’s what MSV’s compositions are – giving all the importance to the emotion of the song. But it is fun to dissect his songs, discuss and analyze. For example, scales-wise, Shankarabharanam/Harikambodhi (with an occasional usage of ma2) was MSV’s favorite. But this combination itself includes a huge number of specific ragas. A large fraction of his songs will fit into this bucket.