Gray units are very situational and I tend to use a dancer over them. Summer Micaiah is like my go to unit for anything as she's a res tank and armor slayer. And also a dancer to omniboost someone
I'm mainly using Jaffar on my main team and that's going quite well thus far. he doesn't always kill and one of my others (Hector) can't always be near him to pick of his spoils, but he usually does what he has to and just deals damage while weakening the opponent if they live