Well, in practice he is head of a design team - no one person can design every aspect of a complex processor, although he may come up with the concepts etc.
And as for 'best' it depends on what your criteria of 'best' is. Best performance, best power consumption figures, best efficiency, best value for money? So many criteria which is why the Intel and AMD fan boys continue to slug it out across the internet.
In reality, mfrs will choose the processor that meets the technical specs for a given application. Personally, I'm delighted to see competition in the CPU market because it drives innovation and keeps prices under control, and so I'm pleased to see AMD have developed what appears to be a viable option for high end machines.