Sure they're both important, Scrump. In an ideal world both will be excellent. However, if pushed for a preference, I will take content over presentation any day, i.e. an excellent song, that has something to say or that can move, albeit sung badly, is preferable to a polished and showy performance of a song that says nothing. Indeed, the latter can be a definition of pop music, for some.

Yesterday morning on the radio as I was driving to work I heard Ronan Keating give an excellent performance of a song with the following chorus: "I love what we do, 'cause we do what we do till it's done; I love what we do, 'casue we do what we do and it's fun". 'Nough said. This morning, same programme, Ronan Keating again singing a different chorus, much more interesting musically too, with very decent lyrics and the refrain "You say it best when you say nothing at all". Both were love songs; same performer; but yesterday's song nearly made me throw up, while today's had me scrambling to find the composer.

In my home culture, all contemporary music is attributed to the composer as a matter of course. Contemporary composers and songwriteres are revered and they have stronger following than the best performers. Don't ask me whay this is so, I don't know. But major concerts in stadia are regularly staged under the name of the composer/songwriter ("a Theodorakis concert with artists X & Y").