Every scalemail project starts with the same fork in the road. Both materials weave the same way, hang on the same rings, and follow the same counts. They behave very differently on your body and your workbench.
Anodized aluminum is the default for a reason. The color is baked into the surface, not painted on, so it will not flake with wear. The finish reads as real metal because it is real metal, and it catches light the way armor should. Painted enamel finishes (like automotive white) add colors anodizing cannot reach, at the cost of chip risk on hard impact.
Polycarbonate runs about 40% lighter than aluminum. On a dice bag that difference is trivial. On a full halter top or torso piece, it is the difference between wearing it for one photo and wearing it for a full convention day. Polycarbonate is also chip-resistant and impact-resistant, and solid-color plastic hides scratches better than any painted metal.
If the piece lives on a shelf or a dice table, buy aluminum. If the piece lives on your shoulders for eight hours, buy polycarbonate and thank yourself at hour six. Mixed builds work too: aluminum where people look, polycarbonate where the weight sits.
Run your project through the scalemail calculator to see the weight difference for your exact build before you order.