Feldspathic or emax for one central incisor? How brittle is the Feldspathic? Are we only talking about larger fractures? (Photo)

The most important person in the equation is a master ceramist. In order to achieve the results you want the crown needs to be fully layered with many different enamels. Those layers are made of feldspathic porcelain. Often we will make a substructure of eMax in an appropriate base color and use it as a core. The tricky part is to get your dentist to work with someone who can handle it. A single central is one of the most challenging things to do in dentistry. My lab is in the office and I think it is really difficult to do it any other way. 

Solid zirconia has no place as a single crown in the aesthetic zone. e.Max can be gorgeous, however, it appears that the e.max crowns you describe had zirconia frameworks underneath. A crown made entirely from pressed and layered e.Max should pretty much get any job done if you match the color and stain it appropriately. Feldspathic porcelain is aesthetically the most beautiful choice, however, it fractures at 1/5th the force required to fracture e.Max. Best of luck!

Feldspathic porcelain is closer to glass than porcelain therefore it's qualities are more able to match an adjacent tooth. The only caveat is that it's the most susceptible material to fracture and you must understand that it will at some point. The next best material is Empress brand porcelain which I recommend. I's stronger but still has qualities that can mimic enamel very, well. My last comment is that if a doctor aims for a zirconia crown in the anteriors then he doesn't understand all the qualities of the various porcelains.PS: your doctor must use an extremely high quality laboratory for color & value matching.