The only Tier 6 I consistently aim for is Zapp. I think the rest really depend on your build. There isn't even a Tier 6 Demon supporter. I think a good and reasonable Tier 6 minion would either be Faceless Manipulator or Faceless Shambler. Personally, I would like to see Hadronox, Gahz'rilla, or even Grimestreet Protector get added to the pool.
Grimestreet Protector would make George cry salty tears... :-P