Dhukk is a beast for progression and dungeons.

Sepulcher is amazing in Clan Boss.

Doompriest and RQ tender both do their jobs just fine at lv50, leveling them to 60 is only needed for CB or when you are pushing harder DT stages.

similar to Airmaxx

Dhukk: Progression/Dungeon/Arena

Sepulcher: Clan Boss

of those 2 get the one to 60 first where you want to improve

Doompriest and RQ as said work well at 50 but of those 2 I'd get Doompriest to 60 first

I would go with SS. CB is the most important thing to progress in, and SS is a beast for CB.

I would argue Dragon20 is most important early game goal.  Think Dhukk and Doom are good choices.

not run dhukk on dragon but i know on cb his AI is messed up and he prioritises provoke which is very annoying.

So the trend is the friend of Selpulcher. Dhukk is already a 60 and mid of masteries... which is a pain :)

But true, I have ok gear, but to reaching next stages I need to improve dragon... 

However, I think runnnin early an ok CB team gets easy drops.