I prefer simple polished cranks, because all the others start to look shabby after a while, and there is not that much you can do about it.

Campagnolo cranks; the worst-looking marks are where the anodising has worn off
More modern campagnolo cranks (in silver finished aluminium) are typically anodised too. Most new cranksets which are silver coloured (metal) are anodised rather than just polished. At least anodising is harder wearing than paint is;

Dark coloured finishes on cranks can soon end up looking like the ones above.
One way of addressing worn anodising (or paint) on cranks is to strip it all off and to polish the whole crank instead. But it is an awful lot of work.
Obviously it is best if nothing rubs on the cranks, but to some extent this seems inevitable. What have other folk concluded about this?
cheers