A good spring steel is one that possesses the necessary combination of properties required for the specific application. Some important characteristics to consider when evaluating the suitability of a spring steel include:

1. Yield strength: The spring steel should have a high yield strength, which is the ability to resist deformation under load. This property ensures that the spring can return to its original shape after being compressed or stretched.
2. Elasticity: Spring steels should exhibit excellent elasticity, allowing them to withstand repeated bending or twisting without permanent deformation. High elasticity ensures that the spring can store and release energy efficiently.
3. Fatigue resistance: Springs undergo cyclic loading, which can lead to fatigue failure over time. A good spring steel should have high fatigue resistance, meaning it can withstand a large number of load cycles without experiencing fatigue failure.
4. Toughness: Spring steels should have good toughness to resist breakage or cracking when subjected to impact or sudden loads.
5. Corrosion resistance (if applicable): In certain environments where springs are exposed to moisture, chemicals, or other corrosive agents, a spring steel with good corrosion resistance, such as stainless steel, may be necessary.

Considering these factors, high-carbon spring steels like AISI 1070 or 1095 are commonly used and considered good choices for many applications. They offer a good balance of strength, elasticity, and fatigue resistance. Alloy spring steels, which incorporate additional elements, can provide specific enhancements to suit particular requirements.

Ultimately, the selection of a good spring steel depends on the specific application, load requirements, operating conditions, and any other relevant factors. Consulting with a materials engineer or a spring manufacturing expert can help determine the most suitable spring steel for a particular application.