Polished!!!! Polished owns chromed. Polished is EVEN FASTER than chrome because the surface is smoother. Slowness won't stick to a polished valve cover. LOL!

If you have to change the color of your valve cover. Please powder coat it. Paint doesn't hold up well on them over time. It might look good for a little while... Wait til it gets oil on it from blow-by or spilled on it when filling it while it's hot. Even baked-on high temp paint flakes. Powder coating is much more durable.