Different varieties of crowns are available. It depends on the quality, material, lab , Doctor and patients condition.

After rct capping is necessary,, type of cap are  metal, pfm,zirconia cadcam, life of cap depends of materials and lab....

Usually RCT causes lot of tooth structure loss weakening the tooth, and hence to increase the longevity of your tooth, to bear normal biting forces you need to do cap. Cap can be of metal, Porcelain fused to metal or full Porcelain. Any of these caps if made properly can last a lifetime. But it is your oral hygiene practice that plays a vital role.