There is nothing that looks better than highly polished aluminum BUT, I do like the new teflon coated wheels.
I hope you mean by painting, you mean BLACK ?
It might look good, depending on the quality of the prep, the care taken when mounting the wheels, if you don't hit anything and if you don't live in an area where there is salt used on the roads.
My vote is to polish first (as JoshT stated geta moths) and see what they look like on the truck, if you like it leave it if not paint it, nothing ventured nothing gained.