Depends on what you have maxed out already. Is your campaign farming sorted out? How far along are you in dungeons?

If I just have to pick out candidates: Apothecary, Miscreated Monster, and Skullcrusher. They'd be pretty helpful if you max them out early. 

I agree with Lxzy. Sepulcher Sentinel, Peydma and Alure are also worth considering, but it really depends on which 60s you have already. 

Thank you for the feedback, it is quite in line with my thoughts. 

I have maxed Kael, Sinesha, Mausoleum Mage, Scyl, Ignatius and Spirithost.

I can farm easily 12.3 on Brutal.

In dungeons, I am blocked at around lvl 14 acros them (except Minotaur that is finished and Ice Golem where I am at 18).  In Faction wars I am close to second boss to almost all factions (except Lizards and Dwarfs, where I have no legos or peic worth upgrading). And I have huge problems in Doom Tower normal, where Scarab King cleans me.  

dont upgrade based on FW, dragon20 is your next objective and overall dungeon progress.

MM

Apo

Skullcrusher

Thank you, Trips! Well, FW is not even second in my interest for the moment, but I wanted to present the best overall view.

It seems everyones favorites are MM, Apo and Skulcrusher.

Actually, if you have Scyl and Maus Mage at 60, I don't think Apo is very urgent anymore, Sepulcher and/or Peydma is more important now. You still need a decrease attack - in Sepulcher's case, single target but with a def aura and increase def, or in Peydma's case AOE decrease attack and also great kit otherwise. 

An AOE decrease defense option would be nice as well, but you don't seem to have any. Or perhaps you have a level 50 warmaiden? Good enough, if so.

Alure would be really purely for Fire Knight - she's a gamechanger there but not much use in most other places. Miscreated Monster is great everywhere and will definitely help in spider (prioritize him for epic books). Skullcrusher, I never really used myself, but obviously AOE counter-attack can also make a big difference in many places.