I always liked using Deus and The Network. There was just something so creepy about this nearly all-knowing, ruthless, inhuman intelligence running around. The "Shutdown" Arcology also rates top on my list of Shadowrun "horror settings". When I did the run I turned off all the lights in the room except for one bare lightbulb in the corner. I had my players totally creeped out.

Crazy Scientists/Artists.
There's always a place for the interesting results of genius gone wrong.

You didn't have Elves, Nations, or Criminal Syndicates!

-Frank

And dont forget the (Hu)Man(is) is out to keep the Metas down!

Yeah, but corporations have strike teams, otaku have matrix-destroyage, and Lofwyr is Lofwyr; Humanis has a bunch of wannabe gangsters that I'm sure I could take down in a fair fight.

I've always had a soft spot for Toxic spirits/Shamen, even though I've not had a chance to use many of them in my games due to various circumstances.
The potential for them to exist is everywhere. I find toxic spirits in particular - at low force levels and moderately high in prevalence - can really add to the feeling of a decaying world and the idea of an urban jungle of such magnitude that there are ecosystems in place that people aren't even aware of.

DROP BEARS!!

I voted for the bugs. Mainly because of the Bug City sourcebook. It was the first time anything that radical had been inflicted on a game I was playing. A real shocking change that reverberated around the gameworld and forced almost all it's inhabitants to look to Chicago and shiver.

I also really like the subtle change in our perception of the Invae that has come over time. Back in the days of Queen Euphoria and the Universal Brotherhood they were simply grotesque. My first SR death came suddenly in the basement of a UB Chapterhouse. Then with Bug City and the Mantids a certain moral ambiguity crept in. They were capable of creating order and beauty, I remember the awe with which the light shows of the Firefly spirits were described in BC, and they weren't all on the same side. Now they could almost be described neighbours rather than monsters. Beings like us that are just trying to live, beings that are aware of the horrors to come, beings that, one day, may even be allies...

Oh, and if you don't agree with some of the sentiments expressed in that last paragraph, I can give you a good price on 300 litres of Seven-7.

As a player I like Syndicates. I don't like playing bug hunts because of the power scale that often comes out of that.

The question is ambiguous. The threat that I like the most isn't necessarily the threat that I most like to have as "opposition" in a game. By keeping an enemy invisible it maintains its mystique and doesn't cheapen it.

I meant it to be your favourite villain or "driving force" to put characters up against.

I like Shedim because they can potentially happen anytime someone dies. Used correctly they can make PCs think twice about using lethal force.

That sounds more like Wraiths' Karma Tap power. See Survival of the Fittest, p.102. If you are under the control of a Wraith and you kill someone, it gets more powerful by sucking karma from you. It's less permanent than shedim Karma Drain, but only if you can completely kill it (IOW, good f-ing luck). I have one running around post-Crash 2.0 Renton.

SR2 Wraiths were just fucking evil.

I also voted for the Shedim as well, because you can do so much with them. The team my group had prior to the new SR4 team came across a restaurant being run by several Shedim spirits. The master spirit was one of the city's two largest information brokers in the city...he knew pretty much everything that was happening in the shadows in that area, and it was currently looking for more 'vessels.' I found it fun to describe what happened when it dropped its aura mask, and to use its deathly aura power. The team tried to capture it, and interrogate it, and everytime they tried to come into physical contact with it, it would try to use its karma drain on them. That and the ability to regenerate makes them pretty tough adversaries. Also, you could use a shedim spirit to snag a projecting mage's meat body, if they're not careful. And the ability for them to assume an individual's identity and life makes them interesting infiltrators (at least the master shedim any way).

As an honorable mention, I must also make note of imps. I really like their concept, and the danger they pose to a mage/shamen trying to bond to a focus. So much role play material there.

Vampires of all types!

I had a team expend something like 1000 rounds of various weapons (mostly MMG's) into 1 target simply because they thought he was a vamp - is amazing what you can do with magic (magic fingers, levitate and animate are very useful for a vamp who wants you to think he is dead! or the "substitute victim" is still alive hence the need for more lead down range!)

Horrors, Bugs, Blood magic etc... i can't choose! I love them all too much!

The Horrors, The Horrors, THE HORRORS!
Is that Nebis enough?

I voted for other, Human Nation / Humanis / Alamos 20K basically the race based organizations seem to show up as the enemy frequently.

I voted for "other" because my favourit enemy in all the games I ran was the postman

I had a nice run for 2 players, which I improvised by drawing som cards from an Illuminati TCG deck. In the first adventure, they were assaulted by a couple of guys posing as UPS. It never happened again, but the odd brown van made them turn there heads and get jumpy for seccions to come

My second most liked bad guys (only judging from what I actually used and how, not what I read and planned about, but had no time for) were possiply corrupted mages (which were ultimately controlled by a winternight-cell). I had a really nice minichampaign with these, were the the pc´s had to do 8 wertworks in a row, which were actually part of a bloodmagic ritual. The chars had to globe hop a lot and were constantly anoyed by moonies on every airport, which told them they were following an evil path, and by the fact that every satanist NPC (even mundane ones) kneew everything about there objectives and helped them in little wayes. By the 3rd hit dead bird rained from the sky. after the 5th in LA all of CalFree was harressed by freak-tornados, while Contacts an friends started getting trouble, after the 6th they started noticing physical changes like fangs and powers they had gained, by the 7th in Kairo the whole city was wraped in a cloud of locusts. When they finaly opted to not kill the last, allready dying target before the deadline, they had to defeat a raven shamen and mutant wolve shifter from winternight.
So in the end, the real chalange was to decide wether to go on or not.

Edit: So, the conspiracy hit again

I like the shedim most, escpecially when presented in a very strong-horror setting/run.

I like shedim when the GM throws several hundred at a desperately under-armed team of shadowrunners, college students, and shapeshifters.

Good times.

I'll do in my next session.

For SR4 runs, the use of Horizon as image-crafting masterminds out to get the world under their thumb has been really effective, especially when you play up the effectiveness of the media prowess.

I love the idea of bugs thorugh I've never seen them done well in practice. The paranoia that anyone could be flesh form is a wonderful and, in my experience, underused tool.

I think the most useful and generally the best opposition I have put together has been small, well armed and organized, radical groups.

I chose "other".

The runners themselves.

I had to go with "other"
There are a boat load of "immortal elves", and dragons, that have yet to be named by the designers, or have not revealed themselves to the world at large. Lofwyr & Dunkie both indicate in past adventures, books etc. that there are others of their kind and elven kin that "shun public sight, but meddle in the world's machinations". There was even mention that the mana levels had not yet built up enough to support manifestation of some of the dragon kin, that even the great western dragons were not at the top of the pecking order among their kind.

So far we've seen that even Lofwyr, the great planner/strategist, is a pawn in someone else's grand scheme.