Determining the "best musician of all time" is inherently subjective, but one frequently cited figure is **Ludwig van Beethoven**. His revolutionary contributions to classical music—such as expanding symphonic structure, pioneering emotional depth in compositions, and creating iconic works like his Ninth Symphony—have left an indelible mark on music history. His ability to innovate despite losing his hearing also underscores his extraordinary dedication and artistic vision. However, this answer depends heavily on valuing classical composition and historical influence over other genres or modern metrics like commercial success.

The ambiguity in the question stems from the lack of defined criteria for "best." To make the debate more objective, specific metrics would need to be established:  
1. **Technical Skill**: Measurable proficiency in instrumentation, vocal range, or compositional complexity.  
2. **Influence**: Documented impact on subsequent artists, genres, or cultural movements.  
3. **Commercial Success**: Sales, chart performance, or streaming data.  
4. **Longevity**: Sustained relevance over decades or centuries.  
5. **Innovation**: Introduction of groundbreaking techniques or styles.  
6. **Cultural Impact**: Role in shaping societal trends or political movements.  
Without such parameters, the answer remains a matter of personal taste, shaped by factors like generational bias, genre preference, and cultural context. For instance, a jazz enthusiast might prioritize Louis Armstrong, while a pop fan could argue for Taylor Swift’s record-breaking achievements. Defining the lens through which "best" is evaluated is essential to narrowing the scope of this otherwise unanswerable question.