Por 15 or powdercoat. Por 15 makes a few colors unless you wanted a custom color and paint is the only option. But, basic black, silver, grey, etc., I'd go POR 15 for the durability from rocks and stuff on the road.
I sprayed mine with black satin caliper paint. Seems to hold up well. Never tried it before other than brakes, so i said what the heck. Used a can and a half.