Metal is always going to be more durable and generally better than plastic - never has and (probably) never will change, at least insofar as quality aluminum and steel alloys are concerned.
Example: Bersa=>Steel mags, steel sights, aluminum frame, metal guide rod=> high quality. Glock=> plastic mag (mostly), plastic sights, plastic guide rod, plastic frame => Junky. Though this is not rocket science, there are nevertheless millions upon millions of purchasers regularly fooled, so it's easy to see that creative & aggressive marketing is many thousands of times more important to sales and the bottom line than quality. Most people would consider these brands in the opposite manner. Marketing.