Tank suggestions for arena

I'm currently running palpatine, vader, nihlus, thrawn and shoretrooper. I was running gk as my tank but decided against it due to him giving bonus speed to opposing vader. I've been thinking about sion because of his synergy with nihlus but mines only 3* until he becomes farmable. I'm open to any suggestions as well https://swgoh.gg/u/bill0207/