After a lot of thinking, I would have to say the sirens are my favourite. Since no one ever actually meets them, their physical traits are unknown and up for debate. I like to picture them with the upper torso of a woman and the lower torso and tail of a shark (sleek and shiny with no scales and pointed edges). Yet another human/animal hybrid. I also like the way their voices are described; a beautiful but sad and lonely sound. I can just hear them singing in my mind.