Saavedro is the antagonist, but is not a villain; what is he doing in this list? He resorted to violence only once he thought he lost everything. He put up quite some Goldberg machines, but nothing lethal. Hideous (in villainous terms).

Veovis is a pawn in A'gaeris' game. Bad enough, but a villain don't allows himself to be second to anyone.

Achenar starts as a genuine ax-crazy beast, but he mellows too much, eventually becoming an antivillain and (ew) sacrificing for his sister.

Sirrus. Now we get to serious business. Intelligent, driven, charming. But he never learned to Write, so could't really do massive harm; he doesn't have a particular grand scheme either. And was defeated by his dumb brother and a meddling Stranger.

Esher is a bit like Sirrus, but calmer. Except when he gloat like a self-respecting villain does. And he loved to skin Bahros, possibly making him a bit like Achenar, too. But he's defeated by the annoying, preachy sister of Sirrus and another random stranger. And start whining once the bahros get him.

Gehn. Grand schemer like Esher. Bad writer, but maaaaybe he was getting better at it in the end. You can dump him on an island of savages with no ink or Books: he will find a way to get back. And he dropped people in the Fissure just to see where they would end up. Took Atrus 30 years and the combined help of the Stranger and the Moiety to get rid of him. Personal favourite.

A'gaeris. Well, he caused the Fall for revenge, the classic of villain motives. Xanatos-gambler, mass murderer, racist enough, name it. Just a little blunder in the end, but it led to a worthy end. On objective terms, A'gaeris is the obvious winner.

And much as I like Saavedro, he doesn't feel like a villain to me, even though he plays that role for narrative purposes.

Esher would be a good candidate, if he didn't behave so ridiculous at the [good|bad] end.

The brothers are simply too shallow and selfish. (Can I nominate young Yeesha, for being the most annoying brat ever?

So I'd have to go with Gehn, as he is the most formidable opponent with the grandest of schemes. Trying to kill your son in order to restore an ancient civilisation. Now that's more like it.

I have to go with Gehn... Out of all of them, he seemed to have the most potential, and thus his fall from grace seems like the greatest waste. Gehn could have been Atrus, he could have grown up in the cleft and learned the lessons of self-sacrifice and humility, could have used his great mind to rediscover the Art, and gone on to create this grand legacy of reviving the D'ni in a new Age of his own authorship... but for his own hubris.

In many ways, Gehn is responsible for Releeshan and the end result of restoring the D'ni--- he taught Atrus, put Atrus on that path. But his great pride was a tragic flaw of Shakespearean proportions, and it corrupted almost everything in which he had a hand.

I've never really seen Achenar as a villain so much as a pawn in Sirrus' plans, especially in Revelation. Having said that, Sirrus and Esher strike me as different types of greedy; Sirrus was originally a dominating man of influence in the ages he and Achenar plundered to accumulate wealth, then during Revelation he plotted to use his sister Yeesha to gain the knowledge of the Art and kill his father (I think he was doing that, I might not be remembering correctly). I can see both of these motives as very self-serving and designed to profit himself. My understanding of Esher is admittedly limited, but from what I gather he seems to be resentful of the fact that he failed to maintain possession of the tablet and very jealous of Watson as he came to use it and ultimately help to free the Bahro. Esher's greed stems more from fact that, unlike Sirrus, he lost his power by his own ignorance, and because it went to another person, more than actually seeking to reclaim the power, he wants to ensure that Watson falls into the same path he did and lose it himself. It's the sort of 'if I can't have it noone can' mentality.

Of course greed pales in comparison to a God complex, this is why I see Gehn as the ultimate bad guy in Myst. It's one thing to dominate the inhabitants of an age for profit, it's entirely another matter to dominate the inhabitants of an age under the delusion that you are superior to not just them but all things around you. What makes Gehn even more unlikeable to me is he bases his claim on a fundamentally inaccurate notion; the suggestion that he creates worlds through the Art, as opposed to merely linking books to worlds. His motives on Riven in the game well meaning, but are ultimately designed to perpetuate this more so, whether of not he would have succeeded wouldn't matter, he would still see himself a God. The very thought does actually sicken me a great deal.

Saavedro is not evil in my opinion because he was exiled by Sirrus and Achenar.

for being obsessed with multiple players solving puzzles...
....Cyan===> Matchmaking trials???
How about more than one choice ?