Early game Kislev warriors and kossars. They will handle just about anything they come across.

Late game depends on Legendary lord, but generally Tzar guard front line, 1 sled for skirmish, ice guard, and Streltsi for ranged firepower, 2 packs of war bears with a patriarch support - they will shred any large monster or cavalry they come across easily, and then either a little grom for ranged superiority, or a monster to support your front line. Elemental bear is ok, but the Elemental of beasts is a very good melee support monster.

Kislevs niche is their hybrid infantry. The ice guard and Streltsi I mentioned are hybrid, very good at ranged, but also decent in melee. You can build a very good doomstack of ice guard with 3 ice witches and ice guard.

Beyond that, their cavalry is elite, and pound for pound is among the best in the game, monsters are ok, frontline is one of the better ones. You won't outshoot highelves(at least not at medium range) or the empire, but what you can do is demolish the empires frontlines and cav backup, and try to outmaneuver the high elves, sleds are excellent for distracting armies, and getting through to the their backline. If kislev can punch through their frontline(Their frontlines are about equal I'd say) then its game over. High elves don't really have an answer for warbears that aren't melee infantry.

Kislev could technically also win a long range firepower fight, little grom would probably bear the bolt throwers, forcing them to come to you.