I'm feeling silly, and have the urge to launch a poll, so go figure.
Classic mermaid - human torso, fish tail
Inverted mermaid - fish torso, human legs
Classic centaur - human torso, horse body
Inverted centaur - horse torso, human legs
Classic angel - human, with bird wings
Inverted angel - human-sized bird (of your choosing), with human limbs (of your choosing)
I figured you should have two options, since it is so hard to choose. Oh, and don't forget to justify your answers - spare no details.