Good beginner heroes are Luke/Kenobi and Vader as much as it pains me to say it for the latter. Now I am pretty decent at HvV and routinely top lobbies but there are definitely way better players than me out there so I'll just focus on the larger modes like Supremacy (where you should start) and GA (where you should go once you get good).
First and foremost I recommend Luke and Kenobi due to Luke's playstyle in larger scale modes of being hyper aggressive and mobile can be a reward, unlike in HvV where playing super aggressive is a bad thing usually. Luke can one-shot groups of infantry with push, can jump while using push, has really good health regen rate (but terrible regen hp value), and he simply shreds infantry once his intensify gets built up. Kenobi is the opposite and is all about defensive offense. Use defensive rush with the Forward! Starcard to get one-shots on 3 out of 4 the base class, and run the health and blocking stamina card (or an All-out push card), and play it slow and steady, with Kenobi you got the stamina and health regen to outlast almost everyone and you should never find yourself with either almost empty if you play right.
For Vader I simply recommend him because unlike Grievous or Kylo (the only other 2 real OP villains like himself), Vader takes two brain cells to use efficiently. Run the 25% Damage resistance star card, Bonus Health, and either the stamina on kill card, the extended choke card (to one shot infantry in choke), or the Lightsaber throw extension card. Vader really is the closest you can get to the game playing itself, 1050 HP + 25% Damage resistance + Godtier blocking stamina and you should never die as Vader in a Supremacy match unless you make a stupid play like trying to swing spam a group of infantry to death as him.
Honorable mentions for other picks include Kylo and Yoda, but these two require a bit more skill to use effectively, as Yoda is SoL if he comes against a good saber villain with support, but he is small to hit and easy to go on streaks with. Kylo has the best CC in the game barring maybe Anakin, but is liable to getting swarmed if your abilities are on cooldown because of the long recharge times.
Aside from those tips and general map knowledge the only other thing you should know are heroes to avoid until you get good with heroes overall. These heroes include imho: Phasma (requires good placement and not being useless camping), Maul (bugged to shit and needs to be played like Luke on crack but with a worse kit), Iden (unless you know how to abuse alt-fire and can roll like a champ, don't use her), Palpatine (some people say he requires no skill but I disagree for trooper modes, against a competent team a Palpatine that doesn't know how to dodge effectively gets shredded), Bossk (all about managing ability cooldowns and picking your fights, really strong on ship phases but requires ALOT of skill to do well with since his gun is ass and he gets melted if focused by more than 1 person.) Dooku (great in hero modes, not amazing in Trooper modes, lacks good CC and range but he can oneshot heavies so that is something to note), and lastly Lando. I never use Lando unless I'm playing against bots or enemies that are worse than bots. His gun sucks at the ranges you wanna be at in GA and CS, his sharpshot is satisfying and good but is his only real strength, disabler is trash (if you jump you can literally avoid it, and normal troopers can just be killed with your sharp shot), and smoke grenade is more of a hindrance than a help.