I have heard a lot of people emphasize how much damage poison can do to the nightmare boss since it is % based.  However, looking at the Reddit list for rankings of champions on clan boss, it doesn't seem the main focus there is poisons so much as champions with multiple hits (for Giant Slayer) and champions with speed boosts (to apply more poisons, hits, heals, etc.

Can someone who is on the nightmare clan boss verify what are the most important things to look for?  I am having a really hard time trying to figure out who is the best to max out for the long run.  I thought since Kael has poisons, he would be great.  However, I see info now that Hordin is better, because of his speed buff he gives himself I am guessing.  And Apothecary seems to be great because of his speed boost, but not sure if I should prioritize him over someone with poisons with speed gear?  And I have absolutely no idea why Athel is ranked so high for clan boss.  Personally, I don't see anything spectacular about her.

What I am considering as far as my eventual clan boss group is this:
Nethril (definitely)

Pain Keeper (definitely)

Apothecary (most likely for the speed boost)

Aothar (most likely because of his poisons)

Last pick is a toss up:  Royal Guard, Hordin, or Marksman (leaning most to Aothar or Royal Guard, but not sure?)

Some feedback here would really help. :P