There is no single metal alloy that is the strongest in every possible way. There's tensile strength, compressive strength, shear strength, impact strength, fatigue strength, fracture toughness, etc. And then there are several components to things like tensile strength. There's the yield strength, where the material begins to permanently deform, which is usually (but not always) the practical maximum strength. There's the ultimate tensile strength, the highest possible stress before it begins to locally fail. And there's the fracture strength, where it completely fails.
The strength of a metal is also dependent on processing. Metal alloys can be made stronger or weaker through production methods (different casting methods, powder metallurgy), heat treatments, and deformation processing.