Can We Say What Diet Is Best for Health?

Maybe not...
As Michael Pollan says:
Eat Food, not too much, mostly plants.

There have been no rigorous, long-term studies comparing contenders for best diet laurels using methodology that precludes bias and confounding, and for many reasons such studies are unlikely. 
...
A diet of minimally processed foods close to nature, predominantly plants, is decisively associated with health promotion and disease prevention and is consistent with the salient components of seemingly distinct dietary approaches.