Specialty Characters to Upgrade

[Muzzleloader]

Can people comment on specialty characters to upgrade/shard with this terrific event going on. Any comments on characters that may be overlooked, especially against tough gauntlet teams. With all the potential skill shards earned some guidance would be helpful on how to spend a few shards.

I found warrior death dog has came in handy with his heals, cleans and permanent death.

[GrimDusk]

Sentinel Corrupt Rescuer is pretty good, along with Assassin Corrupt Droid.