So as a funny note, I also have a character with memory problems (and power loss) who is seeking answers.
The Krae, but only one of the personalities, Jesin Agi. Also an alchemist.
But in line with wha tyou were asking for, it may depend on what type of power enemy you want.
Rocho krul is my force trained trando and first character I made (salis soon after). He's very aware of presences in the force, so it's plausible he had learned of the sith lord in advance since it's likely easier for him to hunt those kinds than it would be for other hunters. He's just out for the jagannath points. One of my more capable characters, has been in wars and is brutally aggressive but adaptable in combat. There isn't a huge range of abilities he makes use of, he uses differing weapons, but has a heavy focus on self enhancement, awareness, and some basic abilities like force throw, push, pull, and bellow.
Nox Kovhorn is an easy option. Not a force user (though he may use ysalimir, we could use that as his backup of some kind as they're in mobile pods). He HATES sith and will kill on sight, bounty or no bounty. Mandalorian with quite heavy armor and typically powerful weapons. Prefers to just take the hit, so he can give a hit. He's arguably less aggressive than Rocho, but that's only because he's typically more ranged. Rocho is most powerful when either sniping or within melee distance, but Nox is more of mid-short range. He can fight at melee, but it's better to keep sith at a distance.
Sinn Shak: Not republic, Rimward Trade League, but definitely more moral then the other two. He's a jen'saarai selkath. Has a lightsaber, but armor and ballistikinesis is a lot of his fighting skill. He's also much more likely to just...attempt assassinations on her rather than attack her outright. Like (if she has a ship) setting it to detonate upon use of the hyperdrive. Or poisoning her food. Stuff like that. Or attempting to regularly undermine her so he can control what ship she gets on, and keep track of her until he finds a safe way to attack her or blow her up.