The Azzies are definitely the most evil fraggers in the corporate world. As for who's got the second spot, I'd put NeoNET and MCT tied, for their fun and games experimenting on technomancers and other digital entities. All the megas are bad on that count, but MCT and NeoNET are the most visible (and most active) of those. Hell, let's do this top ten style, yeah?
Mirikon's Top 10 Most Evil Megacorps:
10: Wuxing - Sure, they've got questionable things, like any corp over a certain size, but they're not nearly as bad as the other contenders on the list.
9: Saeder-Krupp - Surprisingly, Saeder-Krupp doesn't really bring much of the ultimate evil, especially not as much as other megas. They are environmental nightmares, and their draconian policies (sorry for the pun) are the things of legend, but that isn't 'evil' so much as the standard megacorporate ruthlessness.
8: Renraku - Like SK, Renraku's got a reputation for ruthlessness that is the megacorporate norm, but as far as 'evil'? I just don't see it for the most part, with the exception of their lingering racism (and by lingering racism, I mean "just as much as it used to be").
7: Shiawase - What happens when you take a family feud and make it a megacorp? The answer is Shiawase. Constant infighting and backstabbing, but they don't engage as much in the truly nasty drek. Or at least they don't get caught as much. They're too busy turning their knives on eachother to do the true nasty, IMO.
6: Evo - They've been doing e-ghost experiments as well, but not as bad as NeoNET. The 'EvoPeople' thing is a bit freaky, though, which makes me uneasy about their true motives.
5: Horizon - They creep me way the frag out. They aren't as out there as others further down the list, but the whole deal about trying to actively control people to be like something out of Stepford Wives or Invasion of the Body Snatchers makes me want to see them go down in flames. Especially now that they're going into zealot mode. Zealots who say "Horizon is good. What is good for Horizon must be good," scare the hell out of me. Give me SK over these guys any day.
4: Ares - The 'all-American' megacorp has become a hive. The guy in charge is under the delusion that he can control the situation. This isn't just like Jurassic Park writ large. It is like someone seeing the dinosaurs wrecking havoc in a major North American city, and then saying, "You know what we need? More dinosaurs!"
3: NeoNET - One of the leaders in metahuman experimentation during the technomancer scare, and current king of experimenting on e-ghosts, the only thing that keeps them from being higher ranked is that the various factions will burn the place to the ground to keep their rivals from getting ahead.
2: Mitsuhama - I'll give the edge to MCT, if only because they've been bringing the evil longer, and they're utterly unrepentant about it. Plus, coming up with technomancer cyborgs just rubs me the wrong way.
1: Aztechnology - When you are up to so much nasty drek that a great dragon has to blow himself up to stop you from bringing the apocalypse, and you've started burning holes in the manasphere all over your country, you've safely locked the top spot.