Where are you up to in most content and what are you struggling with? If you are keen to make progression on a certain area I think you should focus on champions that will help in that space.
Deliana and Rector Drath are two very good options, but if you are struggling with Clan Boss then neither of these will help much on that front in my mind. Instead, someone like Sepulcher Sentinel might be a better option for the AoE increase defense, decrease attack, plus the chance to null damage. Grizzled Jarl is also a good option for CB.
Where are you up to with CB, Dragon and Arena?
You have all damage dealers plus Vogoth. You may need speed boosters, debuffers, revivers, CC, healers etc. Really any solid champ fitting those roles will help your account at this point. If you're thin on Epic and Legendary books, Apothecary may be a good choice, and so is Reliquary Tender. Deliana is good, I love Psylar in a Stun set, Uugo and Rector are top champs. Take a pick.
I would say
Deliana, Uugo or Rector draft.
Deliana for the leech in CB
Uugo for generel utility
Rector draft to keep you alive if you struggle in content - mostly doom tower and places you are stuck.
Sicia is another great champion but probaly one that can wait till you want to clear things faster.