Just want to point out that IG88 is great for almost any team. None of his skills rely on other droids being around, and if you run an AOE debuff team, is damage gets downright insane with the damage buffs per debuffed enemy.
he's so low health that he blows up too fast. I guess if you run an AoE team, but I don't know why you would since it's the 2nd hardest team to farm next to a jedi team (which is almost pure chromium...).
felt like listing the other best "farms" IMO:
Cantina (energy):
Geonosian Soldier - Available right from the start, this guy is fairly secret "OP". Lowest cooldown on the assist call after leveling some, hit pretty damn hard, but most important, is incredibly fast. Combines insanely well with Phasma/follow up teams and can often erase a threat before it even gets a chance to move.
Jedi Counsular - incredibly solid choice but does trail off at some point. Will still be incredibly useful for Galactic War regardless so worth investing some in.
IG-86 - For the droid team and general use. Not as fast as Geonosian Soldier or as high HP but crits pretty much all the time.
Kylo Ren - Mostly for Phasma teams but he's got a great kit IMO just a tad on a weaker side.
Cantina (shard):
Poe - He's very fast taunter. He may only protect your squishies for a round, but that's all you really hope for honestly. Expose debuff is great too. Plan on seeing a lot of this guy very soon.
Boba Fett - Pretty much only exists for his leader ability. The good news is you don't need to star him all that high because the leader ability is all you're really looking for out of him.
555's - counter-based teams. The speed debuff is fun too, also works for phasma/follow up burst teams.
Daka - incredibly overrated IMO. The revive is very low and doesn't prevent "star" loss in PvE. The heal is kind of trash and doesn't always rez (the AI will also use it the instant someone dies, even if everyone else is at full health and it may not rez at all). The stun/double stun chance is nice, as is the speed, but when the procs aren't in your favor it's sad times. I've had few issues completing dark side levels without a healer (currently mid way through 6-hard), you're much better off going full offense + stun IMO.
GW:
Luminara - Just do it.
Poggle - great buff/support, doesn't really need to be max stars.
Phasma - can be built around, also doesn't need to be max stars. In fact, should probably stop at 4 maybe 5 to start farming someone else.
IG-86 - alternative to cantina farming.