I'm indifferent-to-friendly towards the elves. I've never seen them in their anti-dwarf heyday, so to me they're just picky buyers. And they willingly come to my fort expecting nothing but a bit of trade, are unarmed and their civ doesn't even react to caravans disappearing, so i find killing them unsporting to say the least. On the other hand, i won't put much effort into keeping them alive when they manage to attract a goblin ambush. Last time they accidentally ran into my minecart grinder, i was torn between embarrassment and annoyance - embarrassment because this was clearly an inappropriate way to greet well-meaning guests, and annoyance because my dwarfs had to spend extra time filing away their crummy wares i never wanted to acquire.
PS - i find the humans much worse trade partners - all the clothes they bring are unusable, and if you trade them too much junk, they take so long to pack up that they're in danger of colliding with the dwarven caravan, resulting in a broken wagon and massive trading messes. I've taken to blocking the wagon path when awaiting the humans in one fort. Makes it necessary to buy some heavy crap so they can take everything i want to get rid of, but it's not like i'm missing out on useful items.