A real normal person. Yeah, that sounds generic and like it could be applied to most MCs, but actually, I barely ever see it done well, and then it's often a huge dislike for me if it suddenly turns away from this.
For example, if they are isekaid, they should rightfully freak out. They shouldn't perfectly know how to survive in the wilderness. They shouldn't be fine with killing whatever they encounter. And they certainly shouldn't just fly along with it. Too many don't ever seem like they actually led a life in a normal world.
This also applies to denizens of a fantasy world. Villagers and citizens aren't killers. Just because you got some power, you don't suddenly ignore the ingrained societal norms.
Character development usually happens far too quickly. They have one experience and suddenly take it so hard to heart that it completely overwrites who they were.
They survived the first day of the apocalypse? Good. Now they can kill without remorse and are master tacticians. Or whatever scenario is given.
They trained for a day? Cool. Now they can apply everything they learned in real-life situations.
I like cool scenarios, but I actually like to see the character being more than just a victim of their circumstances. I want their personality to matter, beyond whatever crazy thing happened to them.
In addition, they should actually start out as normal. I absolutely can't have it if it's later on revealed that they were the child of some deity all along, so their path to grandness was destiny. So many "twists" made them suddenly some more-than-mere-mortals entity.
Chosen One plots are boring.
