What are "good" kills? Bandits certainly aren't, as by killing them you get labeled as a killer or murderer.
The reason for this is, that the entity-list isn't updated to the point, that, as soon as someone becomes a criminal to said civ, he is labeled as enemy (prior to 0.40 this was the case) and the entry "former member" doesn't mean anything to anyone.
You could tell someone who isn't part of the civ of the dead bandit.
He won't call you murderer.
He won't spit.
But he will not care either.
Night trolls/megabeasts are good, Actually (bandits are a mixed bag now though), if they are just a random bandit no one knows no one will "like you more" for it usually, which is irritating, but the lord certainly will care if you tell about the leader you killed (in my experience). btw, a lord only needs to know of a kill you had (of any intelligent creature, including people they knew) no-body bandits included and you *usually* can become a hearthperson afterwords.
You get a rep as a hero for rescuing people/prisoners as-well.
In df "killer" and "murderer" mean wildly different things, killer means you killed someone, murder means you killed someone they cared about. If you kill a lot you can become a "Known" or even "infamous" killer or even "a villain" if you start killing important nobels. Your reputation will show up in the legends mode screen about your character and people tell you your rep if you ask them about yourself.
Theres alot of different variations.
Also as i said "it was inevitable" will still usually result in a hero/killer/enemy combatent reputation depending on the kill, toady just hasnt coded in better phrases yet.
You can become a hero (and any variation of it), , dancer etc.
There should be a wiki artical on this but we would have to gather data about it.
Killer is usually a "positive" reputation by df logic which is counter intuitive i know.