Playability and preferences
Playing style and personal preferences make a big difference in what is good playability in a guitar. For some, the string height (also called 'action') must be the smallest possible. For others, a stronger style of playing may lead to buzzing if strings are too low. As a rule of thumb, at the 12th fret, a space between the string and the fret of around 3mm for the first string (high e) and 4mm for the sixth string (low E) is considered standard. I'd advise novices to aim for that, while more advanced players can order a specific string height.
String spacing can also influence playability. Normally, classical guitars have a nut width of 52mm, with 43mm of string spacing. In romantic and early modern instruments, smaller measures were common and suit the repertoire. A modern classical player might feel tight in smaller string spacings, but for some players that are migrating to classical from steel-stringed guitars it is more comfortable. In very specific cases, a wider neck can be a good option, especially for music that relies on intricate chords, as in some styles of Brazilian music.
To complete the trinity of playability in classical guitars there is the neck shape and thickness. Classical instruments do tend to have a thicker neck when compared to Western or electric guitars. It is like so not only because of tradition but also due to playing style and construction. Traditionally, classical guitars do not have truss rods, so they rely upon thickness to maintain the shape of the neck over time. My guitars typically have a neck thickness of circa 21,5mm at the first fret, getting slightly and progressively thicker towards the heel, reaching 23mm at the 9th fret. Those measures can be tweaked on customer demand.
Neck shape is often a hard topic to convey preferences: it is a matter of what feels right in the hands, and it can be hard to describe or even to understand what feels better or not and why. In modern days of guitar production, many manufacturers have used letters to represent a crosscut view of the neck shape: C, D, U, V. I find they can be useful, but nothing ever replaces the experience of having the guitar in hand. The best way to ensure a neck shape that matches your preferences is to try it mid-construction or to refer to another guitar's neck you are comfortable with. We then can measure and profile its characteristics to suit you best.
Nowadays, there are other features that can improve ergonomics and comfort in your playing. Variations on the body of the instrument, the fretboard, or other attachments like an armrest are not traditionally part of the classical guitar but have gained popularity, conforming a line of instruments that some manufacturers call 'fusion' or 'modern'. Such features include raised fingerboards, cutaways, armrests and arm bevels, curved (radiused) fingerboards, and more. Please refer to the Customization page to explore all options available.