Semantics.
The words "cute" and "sexy" can have several definitions to me, depending on how they are used.
When I think of Cute vs. Sexy in physical build, excluding the face, I equate cute with short and flat-chested, and sexy with tall and curvy.
For the face, when I think of cute, I think of a somewhat rounded face where she still has a little baby fat in her cheeks, like the girl in this picture:
. A sexy face, however, conveys an image where her features are distinct and all the baby fat has melted away.
Finally, there is the scales. Ugly, Average, Cute (or Above Average), Attractive, Pretty, Beautiful, Sexy, and Gorgeous.
So it really depends on what you mean, and I'm sure I haven't covered it all. My first girlfriend, for example, had a cute body and a sexy face. Overall I'd have to say she was Pretty and her personality was primarily cute but often teetered on sexy.
Take your pick.