Excellent combo, I would max both of them and hit everything I can

@Mdubbs818   ........Who is in your budget unkillable team?

For UNM its Maneater, PK, Kreela, Occult Brawler and Bulwark. For NM, it's the same team with Kreela slightly adjusted and then the stun target gets switched out based on affinity (Bulwark, Cagebreaker or Frozen Banshee). Cagebreaker and Frozen Banshee aren't the best Stun Targets, but at the time they were the best candidates. 

I need to stock up on silver and get better gear to squeeze out more DPS, so that's what I am working on now. 

I see comps with Duchess as the lead. It looks like with the right gear, champs and speed tuning, I could make a better team, but I don't have the means to make that happen in the near future.

Both Champions are truly amazing.

I guess the question I have is the following:

What does your Arena + Tag Arena teams look like?

If I am farming bots in Arena it's HK -> Ghostborn -> Kael -> Zagara or Tulvold. If I am trying to go against a serious team it will be HK --> Maddam Serris --> Kael or Shirimani --> Tulvold. I will replace HK with Arbiter when she's leveld and geared. Defense right now is usually one of those comps, which doesn't exactly work. I will likely have my defense be Arbiter -> Duchess -> Tayrel or Ghostborn -> Kael or Zagara.

Tag Arena I don't get too involved in outside of daily quests, which means I usually float between bronze 3 & 4. 

Duchess is better imo, but both very good. Since you've completed missions I'd say whoever is better for doom tower maybe.

Arbiter has 30% Speed Aura.

It will be huge for you based on what you said about your Arena team.

Duchess has speed Aura (not as high) but for everywhere. 

I think regular arena will stay as is with bots permanently. Plarium just said eff it, they aren't smart enough for real fix. And its probably not worth it. Focus is on end game/ new content for more $$$

I leveled and fully ascended both. Aribter will be fully booked and Duchess has her A2 & A3 booked with her A1 at 3/5. Right now I have the gear to make Duchess viable/useablefor all areas of the game except  CB (so her masteries will reflect that sort of setup). I don't have the speed gear to dump into Arbiter at the moment (all of that went my CB teams).

For now, I will have her on standby and feed her my best speed gear as I acquire it.  Just let me run Dragon 20 a few hundred more times....