What is the name of a premium tequila known for its high quality?

Don Julio is recognized as a premium tequila brand that exemplifies high quality in the world of spirits. It is made using 100% blue agave and is known for its smoothness and complexity, which are critical markers of high-quality tequila. The production methods, which often involve traditional techniques, contribute to its exceptional flavor profile and overall reputation.

In contrast, the other brands mentioned focus on different categories of spirits. Jack Daniel's is a well-known whiskey brand, primarily recognized for its Tennessee whiskey. Smirnoff is a prominent vodka brand, while Captain Morgan is famous for its spiced rum. All these brands excel in their respective categories but do not fall under the tequila classification, which is why Don Julio stands out as the correct answer when discussing premium tequila.