You tell me....
I know that the game (GTA4) makes it clear that you were or weren't supposed to kill certain people. AFTER YOU DECIDE!!!!!!!!!!
I think we lack such a list on the wiki, so i am asking of you to research it and edit the list.
This is what i know/think:
Playboy X- Kill him, he's a douche and you get house
Dwayne's girlfriend- keep alive so he stops bitching.
Guy Francis wants dead: kill him so Francis stops bitching.