I think that heels look sexy it is necessary that you are able to walk safe with them.
A girl that is wobbling around with her heels does not look sexy at all.
Therefore better lower and safe then high and wobble.
Another thing is, that in my point of view not only the height but also the shape of the heels are important of the look.
Better a thiner heel with 3" then a chunky 4" heel.
Thinner heels seem to be higher then chunky ones with the same height.