Well Rocho is a hunter/trained force sensitive, if he were paid to kill them he might if it looked worthwhile. (Worthwhile can include that the person has powerful allies nearby, not just that they themselves are powerful). But if it looks like an easy kill he's not really all that interested. Depending on what you need Rocho does have an NPC team, otherwise its mostly just him and occasionally a combat droid. He can come either in his smaller ship The Challenger, or if its dangerous enough may have his carrier the Robbers Crown nearby.
Under the right circumstances Vash Walker would do it, either directly or through subordinates. He's my alchemist/mad scientist. Not as outright skilled in combat as Rocho is but his entire method is different. He'd likely only kill the force user by accident (such as if he tried to capture or experiment on him) or if he was causing him problems for Vash. Vash is still fairly powerful and skilled, and uses alchemy and subordinates, to further increase his chances or avoid being personally involved at all.
The last option I have is Salis Marai, more powerful and skilled than the previous two as long as the force is present (if we exclude alchemy as a skill), but more of a niman/ataru fighter with a little extra telekinesis. Rocho tends to swap between ranged and his lightsaber axe only using basic or enhancing force abilities, while Vash has a wider range of choices but tends to only do one at a time. The issue here is that she's a Major in the Zweihander Union, so she's not going around murdering random people. But if they got into an actual fight with her (she usually gets along well, but if they were breaking Zweihander Laws too much or something she'd take action), she has no personal issues killing them.
Some notes:
"Trandoshan Bounty Hunter" doesn't exactly strike any particularly rare cords with people. The only really notable thing to track him with is the Robbers Crown as its a unique ship filled with droid fighters, or if he actually uses the axe. This could make it harder to follow him. Rocho is also really good at recognizing presences in the force, and uses it regularly rather than recognizing by a persons physical appearence. So he's much more likely to spot out people he's known before without being in line of sight. So sneaking up on him isn't exactly easy. But, at the same time, if they've gotten that close it probably isn't hard to get people to say where he went.
Vash is probably easier to recognize as he looks like a human and has a recognizable personality and appearence. And wouldn't be hard to find in a crowd when they realize he feels like two force sensitives in one place (due to a certain organ), something he doesn't right now know how to hide. So he would be much less of an issue to follow, but he still moves a lot. Of the three, he's probably the worst person. And is pretty much cemented in the dark side.
Salis is easy to find relatively. Another human, usually armed, easy to describe. And a Major in the Zweihander Union. Not too difficult it's more a matter of finding her outside of her job and then attacking if that's the plan. She's also a great deal more cautious than either of the previous two, in spite of having almost no fear of death personally.
So of the three in order of immediate combat skill (including force):
Salis
Rocho
Vash
Raw force power:
Salis
Vash
Rocho
Salis has the most skilled subordinates on land and is allied with a faction so naturally has bonus protection while in territory, Rocho has the best advantage in space of the three for combat, Vash has the most range of what he's liable to use to his advantage such as alchemic weapons, self made species, or individual subordinates.
