Vicario is a (slightly) better keeper, but Kinsky is more suited to the brand of football De Zerbi wants to play. For me, the differential is that Kinsky might pull off a great save every now and then (if he hadn't against Wolves, the mood would be quite different) while Vicario's passing isn't likely to improve in the short run.
That's why I'd stick with Kinsky until the end of the season. If we stay up, I hope the club will finally overhaul the playing squad and that would mean getting a new number one, but I think Kinsky has done enough to deserve a loan to a decent side next season.