The one on the left, because the giraffe's neck is long, not its torso.
The question I've commonly heard about centaurs is whether or not they qualify as insects, because they have 6 appendages. But since centaurs presumably have a vetabre, that would disqualify them as being insectoid.
My head canon is that a centaur isn't actually half man, half horse. It's simply a parasite that looks like half a horse. It uses the body of whatever species it can find (traditionally a human) to make the upper half of a body, and controls its movements through the lower half.