Powdercoat will mimic the texture of the surface beneath it. If it's pitted, the powdercoat will not do much filling. Paint allows you more opportunity to correct a pitted surface. A high-build primer or sprayable Bondo like Slick sand can make a pitted frame look mint. It will take more time/labor/$$ than powdercoat. It really depends on the condition of your frame and what your desired result is.