I always used inverted with a flightsim. It feels natural to me every time, but that's with a joystick where the physical action of pushing the stick back seems to translate better to the vehicle moving up.
My brain can't deal with that in a standard FPS though. Non-inverted every time for me there.
I was a hardcore arrow key aimer/mover and didn't use mouselook till sometime during Quake 2 when it just clicked that it was easier. I still used arrow keys for movement till Morrowind I think, when a lot of the other keys were sat around WASD so I finally learned to use them.