So here's a threat analysis of the various enemy factions, from what I believe to be the most to the least dangerous to us on their own, using the classical interpretations of them and what their powers are. If I Just Write is going off of standard and adding his own twists, these assumptions will of course be wrong.
1) Aliens. They start out ahead of us, as far as technology goes, and have immense resources, a interstellar empire of who-knows-how-big. While we will eventually catch up and surpass them, as far as Tech goes, it will be a while, and even once they do they have the advantage of a far larger resource base. They also seem like they would have the largest potential for growth, with their advanced technologies they will probably have a far easier time integrating the abilities of the other factions than any other faction other than us, and their resource base will allow them to dedicate far more resources to said integration.
2) Cultists. We are messing with probably literal gods here, so yeah, they are have a immense ability to be dangerous. We don't want Cthulu awakening and casting a veil of Madness (not the fun science kind) across the world.
3) Wizards. They are just fucking with reality, so until we get to Meta-tech (which seems like rather high up the research tree), there's a very real chance that their spells or what have you can completely ignore whatever protections we invent. Like one quest said, they don't hit hard, they hit weird.
4) Vampires. Rated as such because in addition to being physically badass and magically adept, they tend to be super old and have amassed a number of resources. However, they tend to have a number of weaknesses which can be fairly easily used against them.
5) Werewolves. Unless they are placed rather far on the power scale, they really don't got all that much going for them. They might have some mystical mojo going on, a number of things makes Werewolves also Shamans, but still doesn't seem to be that big of a threat.
6) Illuminati. They are mortals, very rich and well connected mortals, but they are still just mortals. Their true danger to us seems to not be anything they can do on their own, but rather their using their connections to collect powers from all the other factions (like a lesser version of the Aliens, but home-ground advantage to help make up for that). If they do that, then their rating would probably jump up to number 3.
7) Dream Creatures. The jist I've been getting about the dream creatures, they aren't even really a faction, mostly just animals. However, odds are there's more going on than we can see, for example maybe there are Dream Creature Hunters who can take power from the Dream Creatures or something. There's a number of ways I can see these creatures fitting into some genre/story plot, but most of them have the creatures themselves not being the threat we gotta watch out for.