Which Ceramic Tooth is Best: Zirconia, IPS Empress or E-max?

Definitely Emax for what you see in the smile (most esthetic), Zirconia for the molars (much stronger, less esthetic).  It does depend on the bite, but generally this is the best scenario. 

I believe this question was posed some time ago, and there have been some new advancements in the field of ceramics.  My practice currently uses Crystal Ultra and/or XircOn Ultra and All of our patients are very pleased. It is a nano-ceramic material-very durable, aesthetically beautiful and strong. The material acts as a shock absorber and no titanium bar is required. Have a good day. 

You will get a much more esthetically pleasing result with Empress or E-Max. While Zirconia is the strongest, it's best for back teeth where esthetics is not as important as strength.

If you have a heavy bite, Emax if not Empress. Zirconium is not that aesthetically pleasing.