What is the most common type of wood used in making quality musical instruments?

Spruce according to Marty Rainey the man who does 'Homestead Rescue'.He waxed lyrical about spruce being the best.

I'm not sure this can really be answered, but...

Violins, violas, and other members of the orchestral string family, are typically made of spruce and maple, with ebony fingerboards.

Acoustic guitars are often made of the same materials (Electric guitars can be made of almost any material)

Ebony, maple, and grenadilla are used for most woodwinds, except flutes and saxophones which are generally brass, which is often plated.

Most brass instruments are made of, well, brass.

The most common type of wood used to make quality musical instruments varies from instrument to instrument, but in general spruce is the first choice for many instruments, especially for the soundboards of stringed instruments such as violins, guitars and pianos. Spruce, particularly Sitka spruce and European spruce, is valued for its strength-to-weight ratio, which provides both resonance and durability.

Maple is often used for the backs and sides of stringed instruments, especially violins, because of its hardness and aesthetic grain. Mahogany is also popular for guitars, offering a warm, balanced tone. For woodwind instruments, grenadilla (also known as African blackwood) is often used for its density and stability.

For percussion instruments, particularly drums, maple and birch are popular choices for their distinct tonal qualities and durability.

https://extension.psu.edu/what-makes-a-good-tonewood-for-musical-instruments