I used a Tecnifibre Black Code 16G (co-polyester) on my K90 so far since the black color is really nice on it (no other reasons). In this time (K90 is in the shop) Weiss CANNON Scorpion 16L will be installed. I can't remember why I bought the Weiss but I am willing to try it.
By the way can you recommend an-arm-friendly string for Volkl and K90? I haven't had a syn gut or multi yet.
I am on the court.