I just want to add my 2 cents, considering this has been something I've been pondering for a while (I dunno enough about Enneagrams to really have anything to offer here):
Kanaya: IxFJ (I'm not sure whether INFJ or ISFJ though. While she does seem to rely on some sensory stuff, she does seem to me like she reads a lot into new situations. Like, even though she claims she isn't an expert in psychology, she seems to spend a lot of time analyzing the future events to come. For instance, when she notices the viewport goes "black" after a certain point in Rose's timeline, she gets a bad feeling about the events to come in Rose's timeline:
http://www.mspaintadventures.com/?s=6&p=004626 Furthermore, manner of speaking is completely brimming with metaphorical usage to convey her point. Not that ISFJs are incapable of using metaphors, but it's simply that Kanaya's usage of metaphor is so copious that the possibility of a Dom Ni should not be eschewed.) And for the record, yes, I am an INFJ. And yes, she is my favorite character, so I may be biased xD;;
Dave: ISTP (I dunno...just a gut feeling, I guess.)
Rose: xNTJ (I'm think more of an Extraverted Thinker than an Extraverted Feeler, because she seems to take a proactive and organized approach to...ah...how she plays SBURB.)
Gamzee: ISFP?
Feferi: ESFP (She seems to enjoy the moment a lot, which strikes me as Dom Se)
Equius: ISTJ
Nepeta: ENFP (Shipping walls? Many possibilities? Come ON, man, she's DEFINITELY a Dom Extraverted Intuitor! xD And just because she's been referred to jokingly as an "autistic troll in a cave" doesn't necessarily mean she's an Introvert! It just means she's a bit...strange? =P)
Eridan: INFP (...I know this sounds a bit odd, but hear me out. Eridan reminds me of a disturbingly corrupt version of not one, but TWO of my INFP friends, which leads me to believe the trend is more than coincidence. His weird melodramatic tendencies and absolutes SCREAM of Fi, basically boiled down in his extremely skewed version of how he wants to view reality. His desire to intensify the magnitude of his relationships--to fill up the quadrants--seems to represent the ultimatum and absolutism of a corrupt Introverted Feeler. He also seems to grasp at straws in his throes of desperation, which also seems like a corrupted Extraverted Intuitor. He just...I dunno. Maybe this is just a sore subject for me, but I have trouble imagining him as any other type due to the disturbing similarities I've witnessed.)
Sollux: INTP (from what I remembered, he seemed very much like Karkat, but on a milder and more Introverted scale. And he also seems like he is a bit similar to Eridan in some ways, but more practical and less melodramatic).
Karkat: ENTP (I dunno why. His proactive yet hair-brained ideas seem to remind me of Dom Ne, and his "AAGHFGAHFGHAGHAGA THIS IS RIDICULOUS" response to everyone's shenanigans seems to remind me of an Introverted Thinking Auxiliary function screaming "DOES NOT COMPUTE")
Vriska: ESTP? (...Aaah. She's too complicated for me to be able to understand very well. While she is occasionally driven by an agenda, the actions she takes seems to embody a more impulsive and "for the shiggles ;::
" kinda approach)
Aradia: IxFJ? (...I dunno. I never was really into her, for some reason. She kinda reminds me of Kanaya, so I guess INFJ. But she seems a little...different, in a way. Detached. Maybe it's because she's dead. Or maybe she's an INFJ and Kanaya is an ISFJ, I dunno. I still feel like Kanaya might be the INFJ here.)
Aranea: ENFJ (I was thinking INFJ at first, but then she showed more Extraversion as the comic progressed.)
Jade: xNFP (I can't quite tell, though.)
John: xNFP? (He reminds me of an old friend, who struck me as an xNFP. But I could be wrong.)
Terezi: ENTJ (Seems oriented towards progress and pragmatic execution, but driven by an inner vision that Vriska is jealous of.)
Tavros: ISFJ? (I dunno...despite his sympathetic portrayal, I never really liked Tavros. So I'm probably not the best person to type him.)