What's the best material for constructing smartphones?

OK firstly I know 'best' is subjective depending on what outcome you want: style / feel / weight / scratch,crack,dent resistance Etc.

So maybe the better question is what material best encompasses all of those things.

Secondly let's try and forget brand-wars here, perhaps imagine we're talking about the ideal next Nexus.

I'm asking the question because people always argue about plastic vs aluminium. To me both have big flaws. So what else is out there? Carbon fibre? Magnesium? New types of plastic?