For me a lot of it depends on the perspective.

• For an FPS, I think non-inverted feels more comfortable. I generally just want the view window to move in the indicated direction, but I understand people that like it inverted.
• If it’s third person, I actually prefer completely inverted (including horizontal). Especially with something like Dark Souls where one stick controls the player and the other stick controls the camera. It’s more clear that the camera is an external entity and I’m controlling the angle, not the view window. It feels unpleasant and unnatural to me to push left and then also have the camera bend to the left.
• If it’s a rail shooter like Panzer Dragoon or something, we’re back to non-inverted. I’m controlling the absolute position of a targeting reticle and I just want it to move to where I want it to move.