My personal preference is either a Dreadlord, Pit Lord, or even the new Jailer. Would be awesome to see this added in possibly as a separate CD for demonology warlocks simply for flavor to replace the doomguards/infernals, considering they are supposed to be the masters of demonic summoning, and It'd just feel awesome to summon in a pit lord for AoE and a Dreadlord for ST.