I've had a while to think about this and respond to this post again and.
Lilith was framed as a 'new up-and-comer' in S3 and still very dangerous in S4, kind of back-and-forth self-directed and being used, and seemed to have all the power and presence that entailed. Lilith seemed, for the most part, completely aware of what Lucifer wanted to the extent of details--understandable, as she's his First Child, except for the part when she realized fully how he'd get it and faltered immediately because she wanted the new world order (like Casey) but she wanted to be in that world. She wanted to kill Dean, corrupt Sam, and follow him as Lucifer into the demonic takeover. She's the mistress French kings use for knowledge and aid but then kill to retain their own power and escape the woman's hold.
Meg was framed as someone who was Chaotic Evil but knew when to hitch her plans to someone else's and go Lawful. A survivalist above all else, a mastermind of tyranny secondarily, she seemed to want--more than just Lilith's "getting to the good part"--to rule, with Lucifer. While Lilith does the dirty work and Ruby does the grooming of the most important factor, Sam, Meg is more down for enjoying the benefits. I have no doubt her Yellow-Eyed father promised her they'd rule (but didn't say how, to the point that she doesn't even know why Dean and Sam are important, and would rather just waste them), and when Lucifer gained her loyalty in her father's stead as second-in-command, it clearly was with this same promise, that she'd have the world at her feet. Meg's an imperialist and Lucifer's promised her her own continent, basically. "Lucifer's going to take over Heaven! We're going to Heaven, Clarence! You cloud-hopping pansies lost the whole damn universe." She's like Zachariah, petty and power-hungry and loyal only to the head honcho cos Mama likes it on top.
This continues when Lucifer is gone; she doesn't think Crowley deserves to rule, would never serve someone without the power of Azazel or Lucifer, and she's scared of the power via relational aggression (HER FORTE) someone she loathes [they seem like rivals in Hell to me, from S5 on] is accruing, so she finds the closest likely Judases in Crowley's employ (and then Crowley's powerful, surviving enemies number one, first and foremost Castiel, the "power where she can get it") to point them toward what she wants done and claim she's "Good" now. Meg's being "kinda Good" is all about survival and defeating her main political rival in Hell and as he expands upon Earth, up until her last moments, when she doesn't care about surviving any more, she just hates Crowley so much that she'd stab herself if the blade came out the other side to stab him too--that's her defining trait the last episode, the cause she'd die for, to kill Crowley because he took away her victory and she'd never bow to him, power or no, to save the only other people who have a shot at doing that if she loses because nothing is more important than that hatred.
It wasn't a case of her following the wrong, unfortunately Evil cause without knowing it and then "learning and growing" after Lucifer no longer controlled her loyalties with his lies. She followed the same kind of cause until her death: her own, led by her own oppressive desires, whether to rule or to survive or to assassinate or to manipulate or rape or to avenge or to retaliate. That Lucifer tricked her by using those desires when he'd never reward them never made a difference in that she chose rule and cruelty, survival at anyone's expense, the most likely victory, and never changed from doing so. The only at all respectable or altruistic thing she ever did out of her own Free Will was acknowledge how doomed her obsession with Castiel was and let him go, recognize he's not and won't ever be hers ("unicorns" aren't meant to be caught, and she and Sam both idealized that "connection" and ignored how it could never last), and still think he deserved to be saved, with his Don equivalent, even mostly just to kill her enemy. (Fandom keeps trying to take that only bit of good anything away from her by forcing Cas to be with her, by romanticizing her predatory "love" instead of her recognition of his choice [his repeated choice] not to be with her, anyway, but yeah.)
Ruby, by contrast, was exploited in her obedience and loyalty and desperation to help the world (and her own) like Castiel was: she was a grunt, not making the same kind of informed choice Meg or Lilith did. It was clear that they only told her so much, that most of the things she did were led by Lilith and loyalty to one side of Hell (I'd bet my left foot that that side involved Meg and Azazel but they were very careful not to tell Lilith or Ruby the whole story and maintain their own power; also that Alastair and Tammi were on the other side as she hated them). It was clear by the way she reacted that instead of wanting to rule, she saw Sam as a messiah of some kind, "you've saved us!" and that she would have cared more about how that salvation happened (and what it did to humans and some other demons), more than Meg or Lilith ever seemed to. Ruby was the only one who seemed to care that the cause or many of the methods were moral (which is part of why I really hate that they killed her right after her duplicitous reveal, instead of letting her choose). She was following orders, like Castiel, and once she realized her god wouldn't save anyone, her precious Sam included, she'd have very likely defected. Ruby thought demons were saved, not about to rule; she wanted, broken and manipulated, Lucifer to save everybody, including demons, humans, and all the in-betweens left in Hell or on Earth, herself and Sam included.
Lilith was the powerful and informed strategist with a survivalist streak, Meg was the petty tyrant always chasing victory over everyone and the spoils (including Cas at first, that last episode, but lol no, she gave up on that when she gave up on surviving killing Crowley), Ruby was the loyal and desperate soldier who just wanted out of the control of Hell, salvation for her and her species, and was given few choices as to how to accomplish that, told the plan was just.
