I disagree. In ESB, Vader is "evil" (i.e., acting selfishly) in that he wants to get rid of the Emperor with Luke's help and control the galaxy.
You know, I didn't think of ESB Vader that way. Maybe because my opinion of ESB Vader WAS overshadowed by the fact that in ANH Vader was the apatomy of Evil. Lucas himself wrote the line "master of evil". He didn't have any goal but to destroy the Rebel Alliance. Well, and take revenge on Obi-Wan after he learned he was still alive. I wouldn't go as far as to call it selfish at the base (aside from Obi-Wan part, maybe). Just evil. BTW, interesting fact, if I remember correctly, Vader doesn't brag about THE POWER OF THE DARK SIDE, just the Power of the Force, which he demonstrates by choking.
But I don't really agree on RotJ Vader. His goal could possibly remain the same as in ESB, but on the other hand, reluctance is written all over his face during the whole movie. Uhm... all over his mask... Whatever. During the first talk with the Emperor, for example, the talk with Luke on the landing platform, it's like Vader is constantly thinking 'am I doing the right thing?' (one of the possible real-life reasons is that Lucas, in his usual manner, didn't think about Vader returning from the Dark Side of the Force until he began working on RotJ itself)
I want to add that this reluctance I see doesn't work well in the terms of OT only, IMO. In the context with PT, it kinda works. I mean, Anakin pretty much got broken with no real goal to live. Betrayed (or 'betrayed') by everyone, he killed his wife (at least injured badly which then led to her death), no children, all what he was doing was in vain. So, naturally he'll be a pissed off machine. Especially pissed of on Obi-Wan who has left him there to die. And then, his son appears, there's some hope that reappears, some new meaning, which leads to Vader going back.
It works even better, in my opinion (I already mentioned that somewhere), if one is to leave in the movie the NEW 2004 DVD Emperor talk as Lucas has put in there, and delete any (two, to be exact, in the crawl and one line in the movie) mention of Vader searching for Skywalker, learning about him from Palpatine. But the last paragraph is fan-edit orientiered, kinda. But the new 2004 DVD scene doesn't make sense without the changes I've mentioned anyway, so Lucas should do it if he wants to keep it in.
EDIT: By the way, one of the things I don't like in RotJ is that Palpatine, the one that is actually interested in Luke taking Vader's place, makes everything to make that NOT happen. Even in a simple 'kill-that-guy-become-my-apprentince' sense. If he kept his mouth shut, Luke could have killed Vader on his own freakin' will.