The Stormtrooper is a decent enough representation of the original McQuarrie painting, but just like the Darktrooper it's just only a step above a 3 3/4 inch statue. It has articulation at the hips, shoulders, neck, one wrist, and the elbows rotate left/right. The head isn't even on a ball joint. The shoulders have the same full articulation that is standard for current Star Wars figures, but since the elbows and wrists are so limited, it's really kind of wasted.
Darth Vader is by far superior in terms of articulation. It has all full articulation at the ankles, knees, wrists, shoulders, and a ball jointed head. They elbows are of the "45 degree" type, but I don't mind these because you don't have to worry about an ugly ball joint in the middle of the arm. He comes with a blue light saber and a laser pistol that fits in a hip holster (not seen because...well, dammit, Darth Vader doesn't use blasters.)
A nice bonus is that Darth Vader comes with two different heads.
However, I don't really have the inclination to try and figure out which head comes from what source. It's not that I can't...I probably have more books on McQuarrie's concept art than most fans (or more than is healthy for a normal human being to have)...it's that I just don't care.