What is the best MTB drivetrain for optimal performance and durability on challenging trails?

The best MTB drivetrain for optimal performance and durability on challenging trails is typically a 1x system with a wide range cassette and a clutch rear derailleur. This setup provides simplicity, reduced chain drop, and better chain retention, making it ideal for handling rough terrain and steep climbs. Additionally, high-quality components from reputable brands like Shimano or SRAM can further enhance performance and durability.