Been playing a ton of HvV (it's my favorite mode) and for funsies I thought I'd make a tier list based on personal experience. Input also contributed by esteemed Resetter
Papercuts
Heroes
A tier (All abilities are useful. Can make pushes and harass enemies with raw strength or utility)
-Chewbacca - Furious Bowcaster turns Chewie into arguably the scariest character in HvV. While active, Chewbacca absolutely shreds enemies with insane DPS. Saber users can't even block effectively, as the bowcaster does some ridiculous chip damage. If you see boosted Chewie, your options are "run" or "dodge like hell". That's enough, right? Well, he actually has not one, but two easy-to-use stun effects, which are high value in this mode. An truly beast character.
-Rey - An extremely solid all-rounder. Insight supports the team and gives her a huge advantage both in 1v1s and acting as a wall due to increased stamina, mind trick can hinder opponents' escapes, and her dash strike acts as a stun effect that's difficult to deal with. Just be wary of saber opponents aware of how to deal with mind trick, and knock them down with a dash instead.
-Han Solo - Detonite charge is a great tool, dealing huge damage with a nice stun effect. Unfortunately, his standard blaster and shoulder charge don't fare particularly well against saber users. Still, can deal huge damage against vulnerable or unaware opponents, and he's a necessary solution to Boba Fett. Steady aim is recommended.
B tier (Generally useful attributes, or strengths that make up for weaknesses. However, these characters lack the overall power level of A tier.)
-Luke Skywalker - While his abilities generally don't mess enemies up to the level of Rey's, push and repulse are great tools to break up enemy team formations. Rush can also be used to evade enemies or close distance. A solid saber wielder, and extremely useful on maps with bottomless pits due to both push and repulse.
-Yoda - Yoda's repulse attack just isn't great in this mode -- you're going to be hard-pressed to actually fill that bar. Still, heal is a useful tool, and Yoda can rush enemies, evade, and deal a ton of damage.
C tier (One or more attributes aren't particularly suited for this mode, leaving the characters unoptimized. Strengths don't make up for weaknesses in a significant way. You can win with these, but it might be an uphill battle and require good teamwork)
-Lando Calrissian - Let's go ahead and establish that his stun effect is pretty nuts, and that's a great thing to have in HvV. Unfortunately, his blaster is a bit weak, and smoke is an underwhelming ability for the mode. Tight coordination with his stun is necessary to have success.
-Leia Organa - Her blaster alt-fire is MVP for this mode, dealing huge damage either to unprotected blaster characters, or saber users with chip. Shield is pretty weak for this mode, however, and flash grenades don't exactly stun enemies. Still a decent pick if the enemy team isn't well-suited to handling her primary weapon.
Villains
S tier (Fix this shit DICE)
-Boba Fett - There are certain maps where Boba Fett is untouchable. What this means is that Fett can camp it out on some random perch while the rest of your team continually throws themselves at the enemy target and eventually kills them. But it's not like Boba can't fight. He has a strong rocket barrage, with star cards to both increase the number of rockets fired and the damage they deal against heroes...in an all-hero mode. Fett also gets a lot of jetpack fuel with the fast-recharging For the Hunt, so even on maps without good camp spots he can stay airborne and outmaneuver everybody. Good luck, heroes.
A tier
-Kylo Ren - Freeze is a top tier ability in HvV, posing little risk to Kylo and opening up the target for a pounding. Pull performs a similar function, and frenzy works wonders as a chasing tool. He's an overwhelming force to deal with.
-Darth Vader - Similar to Kylo's freeze, force choke exposes targets for a total beatdown. While choke leaves Vader more vulnerable than Kylo's freeze, he makes up for it with a strong lightsaber throw that bypasses characters' guards, and an insane HP pool. Focused Rage is a decent buff that gives Vader an edge in saber 1v1s that aren't against Rey, or against any composition of characters on the flank. Dude's a total tank. Also, his choke can just kill you on maps with pits, so watch out for that.
B tier
-Darth Maul - Maul makes up for a general weakness to blaster heroes with a saber spin that works for both rushdown and evasion. Maul's choke can ping-pong enemies into your teammates, or simply clear them out of the way (and even off the map). Lightsaber throw works similarly to Vader's as a good tool for bypassing blocks. Just watch out for blasters.
-Emperor Palpatine - Do it. Despite some squishiness, Sheev is potentially the best flanking hero in the game. Lightning is an uninteractive source of damage, and dark aura really messes up players he gets close to. Electrocute is a potent stun, and chain lightning is a fine cooldown attack. Proper utilization of cover is necessary to help Sheev stay alive, but skillful play is rewarded with fast, unavoidable damage output.
-Bossk - Everyone dies to grenades. On maps with doorways to hide behind, Bossk's gas grenades and proximity mines really shine. A bit weak in close quarters against sabers, so be careful.
C tier
-Iden Versio - Personal shield isn't particularly effective in a mode filled with saber users, though Iden can hurt 'em by lobbing grenades. Pulse cannon is also a great long-range tool, and she has a valuable stun.