I like Daddario Helicore heavy gauge. Some people like to use a Thomastik Spirocore C string instead of the std. Helicore C string. The Helicore C string seems ok for me though...
I have some experience with strings for making 5 string violins. the standard issue which I prefer is Prim green (medium, bright sound ) or brown Orchestra gauge strong, more gutsy. My C string favourite is Thomastik spirocore type 333 1/2 S this is a 3/4 scale Viola rope core string with silver wrap, so the playing length is right for a 4/4 violin. see more about the violins I make at www.StringAmp.com Best, Michael.