Determining the "best" high-speed steel (HSS) depends on the specific application and the desired combination of properties. However, there are several widely recognized and commonly used high-speed tool steels that are considered top performers in terms of hardness, wear resistance, and heat resistance. Here are a few examples:

1. M2 steel: M2 is one of the most popular and widely used high-speed tool steels. It offers excellent hardness, wear resistance, and heat resistance, making it suitable for a wide range of cutting tools, drills, and machining applications.
2. M42 steel: M42 is known for its exceptional wear resistance, making it a preferred choice for applications that involve high-speed cutting and heavy loads. It contains a higher percentage of cobalt compared to M2 steel, which further enhances its performance.
3. T15 steel: T15 is a tungsten-based high-speed steel known for its outstanding heat resistance and ability to maintain hardness even at high temperatures. It is often used in applications that involve high-temperature cutting, such as milling cutters and broaches.
4. M4 steel: M4 is a high-speed steel that excels in toughness and wear resistance. It is suitable for demanding cutting applications, particularly those involving hard and abrasive materials.

These are just a few examples, and there are other high-speed tool steels available with their own unique properties and advantages. The choice of the best high-speed steel depends on factors such as the specific application, cutting conditions, material being machined, and desired performance characteristics. It is recommended to consult with tooling experts or metallurgists to select the most suitable high-speed steel for a particular application.