I've had people tell me to always keep in in the middle of the back of the neck, to keep it at the top/bottom, and now I have no clue. Is there like a set place to put it?
It depends, when you barre chords, you don't put it up your neck, it's quite hard, but, when you play open chords, it's very easy to use your thumb to mute some strings.
Where ever is comfortable for what you are playing.
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Put your finger wherever you want...

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classical tecnique is to keep it at the middle of the back of the neck, opposite your middle finger. the idea behind this is to be able to move up and down strings easily without having to move your wrist and arm too much.

but i think that as along as you maintain that economy of motion, the exact placement of your thumb isn't all that important. find a position that doesn't limit your motion, one that you can move around on the strings without having to move much more than your fingers.

try the classical method, try wrapping it around the neck, try a bunch of different positions and see what works best.
ya i had kinda the same question ive always read that but your thumb between your first and second fingers in the middle of the neck.. and then ive read to have good technique you need to have your wrist straight not crookked but its not possible with the classical position. any help
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I have been having alot of debate with my course tutor over this recently. When I play, I occasionally place my thumb around the top of the neck and he says this is incorrect, which I do not agree with at all. It doesn't limit my playing doing it my way. He plays classical so he would say that.

I say, whatever feels comfortable and you can play accurately with is the way to go
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