Depends. Crowns are fabricated of different materials by different laboratories or in house Cerec devices. Popular today are tooth colored zirconia crowns which are as strong as metal and tooth colored to boot.
Discuss with a DDS. There are a number of factors that need to be considered when making this determination, including comparative strength and durability and overall appearance. You can have a discussion with your dentist about which makes the best choice for your situation.
Depends. The decision as to the "best" material for crown fabrication is of decided by function, the shape of the opposing teeth, and the opposing material (natural tooth structure or one of many restorative materials). Talk to your dentist about the choices available to you for a specific restoration.