A Smith K or L frame, 4" gun loaded with 38SPL ammo. They can spend HOURS dry firing, opening and closing the cylinder, and in a day or so, have the operation of the gun figured out with ease. That's the first CONFIDENCE BUILDER. Then we go on to loading and live firing while focusing on fundamentals. Trigger pull/press, front sight, nice and slow and easy. Once the are comfy with the 10-12 LB DA trigger pull, we can move onto other things.
Once they know the smell, the recoil, the noise, the use of sights, all the stuff they need, those are no longer "unknowns" and they aren't so intimidated when they branch off into guns with more moving parts.
To someone who has never fired a handgun, giving them an auto loader with buttons and levers and removable magazines and moving slides is intimidating. Their focus on fundamentals is lost in the worry of pushing a button or flipping a lever they're not supposed to.