I recommend a simple bolt acton.22 simply because semi autos tend to go through ammo fast and a bolt actin makes a person think a bit more for each shot. This sis especially important for the novice which, whom can get a bit over excited when firing one shot after the other with it much thought, Ive trained a lot of people to shoot , and fewer mistakes are made when forced to think over each shot.
I'll tell what teaches trigger discipline ,,, an old .22 cal. Benjamin pump rifle. Having to pump that thing 5+ times to get some distance. You pick and choose your targets ,,, and take your time to make the shot count.