I voted for composition and lyrics, though they all matter.
There are songs I like only for the lyrics and that before I listened to carefully, I even hated, lol. And there are songs that aren't much lyrically, but instead have a killer melody.
Usually, the voice matters a lot to me as well, I rarely listen to an artist whose voice I don't appreciate. Yet, it can happen, lol. And besides, there are many artists whose voices I absolutely LOVE (Beyonce, Mariah, Christina Aguilera, Prince), but I never listen to their music simply cause it doesn't say anything to me. (I'm hard to please :lol: )
This is why I appreciate artists who write everything (music, lyrics etc) themselves most - they are capable of combining all these elements and come up with something good (I'm talking about the case where the result is a good song :lol: ) It usually turns me off if I hear that for every different element from a song there was a different composer. It's like instead of listening to a story, I have to distinguish a larger number of stories.