Kobolds: I don't mind them. Generally by the time they start nosing around my militia is more than capable of gutting them like a cave fish, though if it weren't for the risk of attack by tribals I'd leave them the odd bit of stuff as gestures of good will; they want my garbage, not my booze, and that makes them at least worthy of getting the odd handout to me.
Goblins: Main draw of the vanilla game, as without them I'd have had have had no interest (as I enjoy raising strong militias and watching them mow the enemy down.)
Humans: Good friends to my dwarves, hauling away junk be it wood, worn out, or metal, and bringing affordable meat-bone packs (in the form of livestock,) and surface booze/seeds. I try not to make an enemy of them, as while my soldiers are generally more than capable of moping the floor with them usually, it means more piles of shit I need to get rid of (and due to erratic placement of magma and my laziness/distrust of moving hot rock, it usually isn't an option.)
Elves: Trade fairly with us and all will be well. We take thier cloth, wood, animals, and whatever else we may need at the time, and they carry away ill-fitting junk that's been screened for wood decor. However if they do anything to draw my ire more than once, and Peace's calls will be drowned out by the cries of elvish dead.
Dwarves: Drunken and oft belligerent idiots given to fits of often physics-defying madness, but I wouldn't have them any other way.