It is undoubtedly peculiar that none wants to be sad yet we look before, after and pine for what is not. Again as P.B. shelley in his magnum opus To a skylark sums up , our sweetest songs are those that tell of saddest thought. There are many sad songs sung by many artists , from K.L.Saigal to Kishore da and many more. I don't believe in the superlative adjective for this particular type of song. But to me Saigal's Jab dil hi toot gaya, Rafi's Kabhi khud pe , Mukeshji's jeena jahan marna , kishore da 's dukhi mon mere, and last but not the least Lata Didi's Mere waton ki logon are some songs that can easily touch the sentimental chord of any sensible person. In bengali basic songs one can find sad tunes.
Regards