Views about greatest southern playback singer viz., ghantasala, kjy, spb, tms, pbs, jayachandran, sounderrajan - who is greatest - factors to be considered - melodious voice, monopolistic status, singing all types of songs incl. devotionals, padyams, slokas; admiration from musicians, music direction capabilities, recommended/conferred highest national awards - who is greatest all time
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If you consider all factors it is ghantasala - he was the foremost in singing padyams and slokas and none could sing like him. The bhagavad gita by him is an example for this which is the most admired one. Padmavibhushan , the highest civilian award was recommended for him, though due to politics, he was given padmasri.