Hi Nick,
I am using VSL libraries only since 2016. What is funny is the fact that I decided to go with Vienna when I saw Guy Bacos' 11 years old video showcasing articulations. He was using the Vienna instruments player 1 (which was already replaced with VI 2). I bought the Special edition Vol. 1 bundle, and after a year, I upgraded to VI Pro. I loved the additional features, and I could not imagine that it could get any better.
Then the Synchron strings came out, and it needed a newer player. I tried it out with the Epic orchestra 2.0 (as Paul suggested), and even though it hadn't had all the features it has now, I absolutely loved it. Personally, I think that the Synchron player is more user friendly.
With the colours and the dimension tree structure, you clearly know which articulation you are using. The time-stretching opens way more possibilities than VIPro. Even though it doesnţ look so, Synchron player is way more customizable than VIPro - the only limit is your computer. You can have as many SltoXF as you want (VI Pro allows only 4 with 2 layers of articulations). Furthermore, I had always problems setting up the reverb correctly with VI. ( there is worth mentioning that you can disable reverb inside SY player and have the same dry sound as in VIPro) I was also surprised how easy it was to make the switch to SY player - it's like switching from Windows 7 to Windows 10. 😃
I know that there are still some features missing that were available in VI Pro (like auto divisi, sequencer, app). But I think that VSL is planning to add more features to the Synchron player, but we have to give them time.
And finally, the most significant difference is in how the instruments react to CC changes. If you have time, download the demo version and try it yourself. But I found that the Synchron Player reacts very differently to Velocity crossfade than the same instrument in VIPro. It is easier to program the note ends with the Synchron player. I don't know why, but it just sounds better. Also, when you ride VelXF up and down, the transition is different.
Hopefully, I have helped.😊
Erik