My personal beliefs:
1. All guns always need care. There is no "set and forget" with guns.
2. All paint, even the most "technical," eventually wears off.
3. Good-quality Parkerizing is as ugly as sin, but offers excellent protection against rust.
4. Good-quality blue, applied over properly polished steel, looks the best. Well, maybe color case-hardening looks even better.
5. Forged stainless steel is usually an excellent gunmaking material, but cast stainless steel usually isn't.
6. Aluminum weighs less than steel, but beware if you wear off its anodized coating. It will turn very ugly.
7. Nickle plate usually eventually flakes off, but "hard chrome" usually doesn't. But my sweat eats even "hard chrome."
8. Bright chrome plating belongs only on the interior of barrels.
Mostly, the choices you name are matters of ćsthetics, not function.