Add items to a collection from the item or from the collection?

I am building a song & playlist manager. Where should I put my join interface, in the song view or in the playlist view?

Is it better to:

1. enter a song's detail view
2. select "add this song to a playlist"
3. select a playlist to add it to

Or:

1. enter a playlist's detail view
2. select "add a song to this playlist"
3. select a song to add.