Actually my favorite Alien design, or more like Alien posture and body shape design are the Aliens drawn by Killian Plunkett. They're slender, gracile, have really long, fine but strong limbs and are digitrade just like the Runner/Dragon (A3), but with the torso and head and the silver grayish black biomechanoid carapace of the original Alien (Giger). If you'd ask me that's the ideal Xenomorph design hands down. It looks incredibly dangerous yet very beautiful; it looks very elegant and delicate yet very strong and tough - both at the same time. It it's humanoid without looking humanoid at all.
...Just noticed that Killian's Aliens don't have the same hind-leg foot design as the Runner/Dragon/Dog Alien. I kind of prefer the latter as they are more elegant.