Actually this is a highly discussed question. Most 3Ders use index and thumb for "more precise control" While most old school pilots use their thumbs. I use my thumbs because thats whats most comfortable for me. I say do what comes natural which seems to be index finger for AIL/ELEV. and thumb for rud/thro. Also on the thumb stabbing. That doesn't happen to me, maybe your nervous and your pushing hard on the sticks without knowing it Although I doubt you would be nervous on a sim.

Low-n-Slow