It depends on which instruments you are looking at, for whom, for what purpose, within what price range, etc. There are so many factors, some of which are more or less important depending on the player and use case. So it really depends on what you are asking, as this is such a diverse and multilayered subject.

Hello, I believe that assessing the quality of a musical instrument involves a combination of technical, acoustic, and ergonomic factors. From my perspective as an educator working with string instruments, an important starting point is the construction and materials — aged wood, proper varnishing, and craftsmanship directly influence sound quality and the instrument’s longevity. In terms of acoustic performance, two key aspects are sound projection and richness of tone; a good instrument must respond dynamically and maintain clarity and balance across all registers. Ergonomics is also essential, especially for children: instruments must be comfortable, well-sized, and adjusted to avoid postural strain or technical difficulties. The setup — including the bridge, strings, pegs, and soundpost — can enhance or compromise performance significantly. Finally, there are subjective elements: the musician’s connection with the instrument and feedback from experienced teachers or luthiers often guide the final decision. In short, quality is not defined solely by price or brand, but by how well the instrument supports the player's musical and technical development.