I use GK currently. And unfortunately. I can't wait to run all DS. My plan is to use KRU once I got a few more stars on him. I have SiT but haven't used him yet. I will try him out soon. Shoretrooper seems to be very beneficial as well. Unfortunately I'm building my shore so he'll be a bit.
Now in no way am I saying they are better than GK. There is no DS tank that is good as GK but I think kru, shore, and SiT all can work well. SiT however probably brings the least to the team overall though. Other than just being a brute with tons of health, protection, and defense.
