The factors to look for when deciding for crowns are mainly based on two things I.e. function & esthetics. Function is when you can properly chew your food with minimum discomfort & maximum strength while protecting the tooth underneath the crown. Esthetics is when your new crown closely mimics the natural anatomy of your natural tooth so that it can enhance the appearance of the patient. Lastly your crown should provide a long lasting & effective treatment needs so that you don't have to worry about anything else. The best quality of crowns available are zirconia crowns which easily fulfills all the above requirements.

Hello chidambaram, any root canal treated tooth needs a crown and if its posterior teeth then you need a metal crown to have a sound tooth. This is function based treatment. If anterior tooth then you need to go by your dentists ' advice depending up on your needs. More aesthetic restoration then it's price is higher.

Zirconium crowns(full ceramic/metal free ceramic ) are more Advanced in the way they are fabricated. (3d printing in raw terminology ) you can expect exact fit and contours compared to metal ceramic crowns. Coming to variations in zirconium I don't find much difference  between the high end companies and the regular ones. If price is not a factor opt zirconium crowns. other better option will be DMLS crowns in metal ceramic. You can expect  the same fit as the zirconium  crowns.