There is simply no doubt. The best plot twists are the ones in the fashion of the 6th sense. The type where you go through the entire story missing 1 important piece of context, and then having that little bit of context revealed just changes how you view everything that has happened up until that point in the story.
Another one I have been reading recently that has these types of twists is a series called Mother of Learning. It actually pulls a few twists of this sort, and the way it's written I'm very sure these little twists were planned from the moment chapter 1 was written. There are 3 things that could be considered twists. 2 of them have to do with the nature of the time-loop they are stuck in. 1 has to do with the MC's abilities.
These twists are pulled off very well to the point that, starting a dozen or so chapters before the reveal, you are actually starting to put the pieces together and suspect it yourself. Just because you can see it coming though doesn't make it any less effective.
Point is, make it a twist that's less soap-operaish and more along the lines of something that just exists in the world and you really could see someone overlooking, but bears some kind of real relevance to the plot. Such as a person having an unknown (but subtly hinted at) power all along, or the converse of that being that they've had some kind of horrible condition that's killing them all along. Or, there is some kind of divine or primordial tier artifact and the main cast discovers something shocking about the manner in which it operates. (Let's avoid anything shock-bait in nature like it running on the souls of ritualistically abused children or something like that. Referring back to Mother of Learning, how about having it crafted from the body of a dead primordial horror with cuthuluesque properties. Equally shocking but far less contrived.)
