I had a pinched nerve way back when, so the tips of my fore-finger and thumb on my right hand are sensitive to the knurled or sharp points at the tips of most sticks (well, most of the ones I've tried). So, I have sort of defaulted to fingers, although my left hand is fine, and I sometimes use thumbs for the throttle. Odd, but I seem to jump back and forth from thumbs to fingers on the throttle/rudder stick.

But, as originally stated, even though my instructor insisted on my using fingers, well, I do so on my right hand only because it is uncomfortable to use thumbs. It comes down to a matter of choice and what's comfortable for you.

CGr.