I spared everyone on my last save, even Clarence (he dies either way), killed Playoby X, killed Francis and chose revenge.
Ivan - Ivan was innocent and Vlad was a nobody, I didn't see any point in killing someone on his orders.
Cherise - again, I didn't see any reason to kill her.
Clarence - I randomly chose to spare him, but actually was going to kill him at first.
Playboy X or Dwayne - Dwayne was a good guy and didn't deserve to die, also, the safehouse you get for killing Playboy is really nice.
Francis or Derrick - I found this one easy, Francis was an annoying, whiny, crooked cop who kept blackmailing Niko into doing work for him, while Derrick was a good guy and a friend (he helps you in Three Leaf Clover).
Darko - Why go through all this effort of finding Darko to kill him him and not feel any better, sparing him is the best choice to make.
Revenge or Deal - I didn't want Roman to die, and Kate is lost either way.