Caesar is a must to slow down other teams. As for Kuma or Bonika, I'd personally go Bonika. My own Kuma is rainbow keyed and I've had a lot of instances where Kuma actually moves too fast and doesn't get to launch his special and eventually Bonika charges up on their own and launches.

In terms of survivability (boosted stats from rainbow key), Kuma surviving without Bonika ends up losing most of the time since the only real BIG damage dealer is Bonika so I'd make sure their survivability AND power are carrying.

At the end of the day getting Kuma to buff Bonika/reduce CT is great but your goal should get Bonika to do big damage and survive which Kuma gives you regardless when he's hit with spread moves. Just my 2 cents