First off, let me say this:
The OP indulged in selective C&P. That was not *all* I said in the first post. He selectively C&P to make his argument sound better.
Now, on to the debate. The OP brought up demons and devils. Nice application of emotional demogaugery there. A bit transparent, but good try. As I said, that is not all I posted in my first post, and that bit of underhanded tactic lent the demons and devils argument far more creedence than it really has.
My stance was that Vader was Chaotic because he could not conform to the lawful Jedi. He gave in to his emotions and it was his impetuousness and emotional rampages that made him fall. Random betrayals because he felt angry and needed to lash out is chaotic behaviour. That is what he did to Padme right at the end.
Selfishness is not a trait of law or chaos. It is a trait of evil. Overthrowing tradition, emotional behaviour, etc., is chaotic.
Just because Vader tolerated Palpy is not a reason to claim he is lawful. Remember that Orcs are Chaotic Evil, and they are described as following the "strongest rule" form of government (this form of government is also described as CE in the DMG). Vader wasn't in the position to challenge Palpy because Palpy was stronger than him or had control over him via the Dark Side (which was one of the quotes the OP listed). He itched to kick Palpy in the nuts, though, to take over, and he would have, except for the pesky power thing. That is how CE governmental bodies work as described by the DMG. That is also classic CE behaviour as described by the PHB.
Just because someone used the Law occasionally is not reason to believe he *believes* in the Law, which is the true sign of lawful behaviour. Vader did not believe in the law, unless he is the law. Most of the Empire's troops were like that (Palleon and that Bakuran guy, Thanas?, were the exceptions, not the rule). They looted, murdered, enslaved, etc., at will across the galaxy, even though, I am sure, if you went and murdered someone, you'd be thrown in a room with 3 walls and bars for violating the law. That is unlawful behaviour.
He doesn't seem like someone who got off on random violence and bullying the weak... he had a purpose and worked within an established system to fulfill that purpose. Any deviation or failure to help him achieve what he needed to achieve brought on threats and death. And Vader had no problem leaving the chase in the asteroid field when the Emperor wanted to speak with him... his emotions and individual desires weren't winning over in the heat of that chase, and really never won over in any other moment of the original trilogy until Luke's impending death by the Emperor moved him to save his son. He's even excited to turn his daughter over to the Emperor so that she can serve the Dark Side. Look at how he interacted with Admiral Piett in the original trilogy. He promoted him over an incompetent superior and though he threatened him, allowed him significant 'failures' and never killed him. Look at how he deals with the heroes escaping at the end of Empire... no raging or killing on the bridge of his star destroyer. Plan failed, but seeds sown. Move on to next plan. Very Lawful Evil if you ask me.
