I am slightly rusty when it comes to all the details, but let me summarize my doubt and mention a few relevant evidences.
Throughout episodes V and VI, it seems as though Vader is seeking to recruit Luke for the Emperor's sake. Not only does he declare that intention in the Emperor's presence, but he also shows great loyalty to the Emperor throughout; he delivered Luke personally to the Emperor and blocked Luke's attack on the Emperor. Even till the very end, he watched on as his son was tortured, as though nothing could ever be more important than loyalty to the Emperor.
This couldn't have been Vader's ultimate intention though, or else it would go sharply against the original canon (now perhaps Legends) narrative, according to which Vader spent every moment of his life plotting against Sidious, and in fact was delighted to learn that he could now overthrow him with his son's help. Not only is this explicitly claimed in "The Rise and Fall of Darth Vader" by Ryder Windham, but it's also reminiscent of what he said to Padme: we can overthrow the emperor and rule the galaxy together, as a family. It would be very characteristic of him.
Putting together all the pieces, I barely doubt that Vader's final ambition was to overthrow Sidious and have Luke by his side. But is there a way in which all of Vader's words and actions in the movies can be clarified in this light?