Truth/Gravemind > Atriox > Didact/Guilty Spark > Tartarus > Regret > Ripa > Cortana
Struggling to separate some of these and my ranking keeps changing the more I think on it, Lol.
Truth and Gravemind are at the top for me but specifically their Halo 2 counterparts, I think Halo 3 arguably ruined them both slightly but Truth far more than Gravemind, Truth in Halo 2 was like an evil mastermind, a deceiving backstabber who let Mercy die, always seemed to have a plan and played the politics brilliantly, then Halo 3 comes along and he sorta becomes...Dumb? Barely has a plan, becomes an old man shouting at the sky, seems reckless and rushed and it ruins his character for me a little.
Gravemind on the otherhand, I love The Flood, I think they're the best villain lore wise, Gravemind in H2 is so damn creepy and oozes atmosphere, an almost Lovecraftian monster which is immediately intimidating, I also love the way Gravemind speaks, Lol. You know he's smart, you know he's dangerous but again in Halo 3, ehh, I think he's still fine but Idk...Something feels different in his tone, it doesn't help that we don't bloody see him, except his tentacles which make him seem weak, his dialogue was better in Halo 2, he makes some questionable choices in Halo 3 such as bringing all his forces to The Ark, why? We was told one Flood spore is enough to destroy an entire planet, he could have sent a few ships to random human colonies which are less defended and created armies all over the Galaxy which wouldn't have taken away anything from his army, he loses his intimidation factor, he's ranting at Chief while Chief just strolls into his bowels and takes back Cortana with ease, Lol, he fails so hard at backstabbing Chief after he aids him to defeat Truth.
Halo 3's story is a rushed mess.
Atriox I do agree was underused in Halo Wars 2 but on the other hand, he steals every scene he is in from his presence alone, I vividly remember his Origin Story which gives us quite a bit on his backstory (who he is, why he formed The Banished, why he is a threat), then his fight with Spartan Red where we see him utterly dominate them, leading the fight to show his troops that the Spartans aren't anything to be afraid of, him keeping them alive both as a warning to leave The Ark while at the same time following them to see where they're located and his entry into Awakening the Nightmare to scold the Brute Brothers, Lol. There ain't a scene which Atriox is bad in so far Imo, he simply needs more screentime.
It could be said that we know a lot about Atriox's character by how The Banished operate too, we know Atriox and by extension, The Banished, aren't trying to make Humanity extinct, they even accept Human soldiers, Atriox tried to avoid unnecessary fights, he gave Spirit of Fire multiple chances to leave, he expresses no hatred for Humanity, they're simply in the way, The Banished species are more on equal terms than The Covenant species were, sure, there's still some bad blood between species and we see that in HW2 and Halo Infinite dialogue but it's not The Covenant bad where they threatened to extinct multiple species unless they signed aboard and there was a very obvious ranking order in The Covenant, Elites and Prophets at the top, every other species is dirt, in contrast to The Banished which has Brute, Elite, even Hunter leaders, one of Atriox's main commanders is an Elite and it seems in Infinite, Escharum is actually friends with Jega which was unheard of in The Covenant.
It will only take for me, I think, one more game with Atriox as the primary antagonist to put him ahead of Truth and Gravemind.
Didact is awesome in the books, intimidating, a tactical genius who crushed armies, in Halo 4 his dialogue Imo is among the best across all of Halo, I frigging love the way he speaks, how he articulates, his monologue at the end of Halo 4 was perfect and his introduction was great too, the immediate tossing aside of Chief without a care for who he is, you could tell this dude is powerful immediately but it was sorta ruined by the end with his crappy boss fight and I sorta feel like for a tactical genius his plans in Halo 4 seemed a little rushed, get the composer, go to Earth, kill all of Humanity, do it in a week, Lol but when I think about it, he would have succeeded and killed all of Earth if not for Cortana's space magic so maybe his plan wasn't so bad...
Guilty Spark is perhaps the least evil of all these characters with a tragic backstory, formerly a human who died in battle, placed into a robot, designated to watch over a Halo ring for 40,000 years all alone, following only protocol set by the Forerunners and logic, he is obviously a psychopath but you can sorta see where he is coming from, he's genuinely convinced he is doing the right thing, he's been programmed to believe that the Flood are so utterly dangerous that the only option is to fire the Halo Rings for the greater good, something his creators did, then a green man in a suit comes along and blows his Ring up in a few days, Lol, it is easy to see why the man is a little upset and frankly, a broken person and his terminals in CEA are well worth a watch.
Tartarus was cool in his scenes, oozed confidence and his design was great too, I wish we saw more of his character though and he's a bit of a naive follower of Truth, not exactly smart in some aspects but he's a worthy adversary to Thel.
Regret is fine, a decent side villain, at least he didn't go out like a punk like Mercy did, I don't have much else to say.
Ripa...Sorry, I simply can't remember him that well and I played Halo Wars 1 for the first time ever only recently, all I can remember is that he looked awesome and he was an Arbiter, I should maybe replay Halo Wars 1, Lol.
Cortana was a bad villain, on paper he becoming a villain is fine, her rampancy is unavoidable but it was awfully executed and it was done too soon after Halo 4 which sorta ruined a lot of Halo 4's plot points.