Yes, I agree with you on the varying degrees of "interpretation" and manufacturing issues that come into play when comparing the heads, but I was talking overall. Still, the teeth, skull and general face details on both NECA and Medicom are more accurate than the HT figure. Anyway,
overall, in proportions, feel and general accuracy of the entire figure, the NECA and Medicom are better, that's all.
As for articulation, as I said, the suit hinders poseability a lot around the hips, but it is what it is due to the nature of the suit, so I don't really have a beef with that. Again, what I found a bit of a let down was the inability to spread out the arms. Which both the NECA and Medicom can do. But then again, the HT gets closer to the "ball" pose, so each has its advantages and disadvantages.
But again, take the HT Aliens xeno, poseability is much better on it than on the Alien version, which isn't surprising since it's constructed differently (and rather poorly
).
And to your point on range of movement HT vs. Medicom, having both I can say this:
Head/Neck: lateral movement is roughly the same for both, the Medicom is slightly hindered by its accuratelly placed tubes. Up and down movement is much better on the HT, the Medicom -although it has a similar range- does not hold the pose. Sideways tilt would go to the Medicom, but it's a moot point because it doesn't hold the pose. HT's doesn't have any tilt (incidentally, NECA's figure has a great range of movement on the head/neck).
Arms: Medicom all the way. The figure has the full range of movement of a Medicom base body. The HT is more limited in every movement except for the wrists.
Torso/Waist: range is basically the same, but the structure of the HT body holds the sideways twist of the waist better. The forward and backward motion is the same on both.
Hips: HT all the way. It can bend much deeper and holds the pose better, the Medicom is a lot more restricted.
Legs: Medicom FTW. Again, the figure has the full range of movement of a regular Medicom body. The thighs have the cut joint, the knees bend almost 45° and the ankles have tilt and swivel movement. The HT has no cut joints on thighs and the knees don't even bend to 90° (at least I haven't tried it for fear of breakage). The ankles have full range of motion though.
So which is better articulated? On paper I would say the Medicom, but it really depends on what you want your alien to do: if you want the ball pose you'll like HT's articulation better; if you want the Lambert hug, you'll like the Medi-culation better.