People seem to like skulls. Frankly I would try something different at this point.
You will want a simplified design that can fit within a square shape with nothing poking out of the sides, streamlined designs are much more popular than sculpts.
People hate really tall caps, try to keep them close to something like an OEM profile.
This community is full of perfectionists. So much as a scratch or bubble and folks will be ****ting all over your work.
Something iconic and symmetrical. As in you can take just the eyes of a Clack, or just the jaw of a Brobot and people can instantly fill in the rest with their minds.
These are just what I like, and while sculpted artisans certainly have their place and can be wonderful, they are distracting and not as functional.