Yes, of syn guts, N.Vy is probably the best. It is stiff and resilient, and works well as a cross.
All other syn guts -- Technifibre, Kirschbaum, etc -- feel about the same to me. I cannot tell the difference. They all last me about 1 week, in 17 guage. This is why I stopped using them. The two syn guts that last for me are Prince TopSpin 15L and Wilson Extreme Syn Gut (both are very stiff).
Isospeed Professional lasts longer, and Gamma TNT2.
Another interesting string for crosses is Gosen Nanoblend (gray/silver color). Of the syn guts I've tried it is probably the softest (* after Forten Sweet). Approaching the soft multies territory. I liked it better than Forten Sweet for crosses, but then again, I am favoring stiffer crosses when combined with poly.
So, I'd say: soft crosses: Forten Sweet, Gosen Nanoblen, Isospeed Professional, and all other solft multies. Isospeed has the best durability of this bunch.
More durability -- Gamma TNT2.
Even more durability -- Wilson Extreme Syn Gut.