I would say type three . They aren’t as into introspection. I don’t think many three’s are studying the enneagram they don’t see it as helpful in achieving goals. I think they only enter a seminar on it reluctantly by a boss or spouse! lol.
As a six yes conflicting traits and relating to other types so easily can make you have doubts about the system.
Eights I agree would reject it as they don’t want to be vulnerable but recognizing themselves as an eight might remove cynicism. There are it seems a number of enneagram teachers and coaches that are eights.
Seven probably don’t get into that deep as a rule but might find it interesting.