The "best" spring steel depends on the specific requirements of the application and the desired combination of properties. Different types of spring steel offer varying strengths, elasticity, and resilience to meet specific needs. Here are a few commonly used and well-regarded spring steel grades:

1. AISI 1070: This high-carbon spring steel offers good strength and elasticity, making it suitable for a wide range of spring applications. It has a carbon content of approximately 0.65% to 0.75% and is known for its durability and excellent fatigue resistance.
2. AISI 1095: Another popular choice for spring steel, AISI 1095 has a higher carbon content, typically around 0.90% to 1.03%. It offers excellent strength, hardness, and edge retention, making it suitable for high-stress applications such as springs and blades.
3. AISI 9260: This alloy spring steel contains a combination of silicon, manganese, and a significant amount of carbon. It provides good strength, toughness, and elasticity, making it suitable for applications requiring durability and impact resistance, such as automotive leaf springs and coil springs.
4. AISI 6150: Also known as chromium-vanadium steel, AISI 6150 offers good strength, toughness, and wear resistance. It contains chromium and vanadium alloying elements, which enhance its performance and make it suitable for heavy-duty springs, torsion bars, and other demanding applications.

It's important to note that the choice of the best spring steel depends on factors such as the specific application, load requirements, operating conditions, and other desired properties such as corrosion resistance. Consulting with a materials engineer or a spring manufacturing expert can help determine the most suitable spring steel for a particular application.