Working on various projects, both as "classical" compostions and as film/TV scoring jobs, I have used different sample libraries, but none of them seem as good as VSL because of two things: 1) the fundamental focus of VSL in recording actual musical values, and 2) the interface developed for that.
So many other libraries have great sounds but are not useable as soon as your music drifts away from whatever they sound good at, out of the box. But with the focus on basic musical values - what exactly the instrument does to play various styles - no matter how "good" it sounds according to a current style or not - i.e. its particular basic legato, staccato, sustain, dynamics, etc. - it is instantly obviously how to use the sounds. And the Vi/VE interface makes it easy by simply switching between them. Choose your manner of switching and go.
I have never used the provided presets and matrices, even though they are expertly programmed, because my approach has been to start with ONE articulation: legato or sustain. Then when working on the piece, realizing another is needed, say, a detache or staccato, or maybe a dynamic, then it is added. But it is a cumulative, simple approach based on one's own music that can be used.
VSL is the only library that organizes sounds in this way - all the others I have used have special organization based on what they figured out as a way of marketing their sounds, but not based on musical values. The people at VSL thought long and hard - how does one represent everything this instrument does with digital samples? They then proceeded to do that. Nobody else has done that.
I find it funny and yet very appropriate how the center of the musical universe - Vienna - is where this technology was innovated and developed. If Mozart, Beethoven or Bruckner were alive - they would be VSL users.