Which team should I work on?

Killbot5000

Neither of these teams are going to be arena killers, but which one is a better 2nd string line up?

Rebel team-
ST Han as a leader
Biggs
Rebel Pathfinder
Sabine
Pao

Or...

Jedi Team-
IGD as a leader
Plo
Ahsoka
Jedi Consular
Barriss

I'm pretty set on who I want for which team, just can't decide who to work on first.

Rotor

Neither... not even galatic war.

evanbio

Neither of those teams are very ideal, unfortunately. You have 2 Rebel tanks, which aren't going to help you much. And 2 healers in your Jedi team who aren't going to provide any damage for defeating your opponents.
For Rebels, I would suggest Biggs and StH. For lead either run Lando (who will help on your heist events and Crit Chance mod challenge) or Wedge (you will want him eventually, but can't recall when he becomes farmable). Sabine is good, but a difficult farm at 1 hard node. You could also include Ezra, who will work on a Jedi team as well.
For Jedi, starting out, IGD lead is ok. He drops off over time, but for starters he's pretty decent. IGD, Ahsoka, and QGJ are a decent group and are pretty easy farms. If you want a healer, Lumi is an easy farm and pretty decent early on. Again, she drops off over time. You could also run Ezra or JKA, and Aayla Secura is another good Jedi, but can't remember when she's farmable. You may want to run a tank with your Jedi, and again STH is a good choice. As is RG. Both are good choices even late game.

Poxx

If u wanna run an IGD lead, it's viable top 50, but not in your configuration.

2 must-haves r Aayla and 5's. Both easily farmable. Both give themselves a 50% damage boost when they counter and IGD boosts them more when they counter.

GK w/ his reactive taunt, group Retribution buff, crit immunity and call-all assist is a shoe-in. Leaves u 1 spot best filled by Ezra so u have a dispel and a hitter...or zzR2 for the cleanse and offense boost.