Skip the .410 too hard to learn to hit with. Other than non moving targets.
20 and 12 ballistics are very close, it's the oz. of shot that's a little lighter in the 20. It's a myth the 20 kicks less than the 12. Typically the 20 guns are lighter than the 12's so felt recoil is the same or more. Chamber a 12 gauge weight gun in 20 and now that's a sweet shooting rig.
With a new shooter you need to keep them comfortable, low recoil, and next consideration is weight of the gun. They have to be able to lift it.
Put them into a Browning gold auto or Beretta 391 gold. Both of those gas operated semi auto guns shoot very soft. Couple that with Winchesters low recoil loads and you'll get them addicted instead of turning them off.
Skip the pump guns. They are the best as far as durability but also kick the hardest. Single shots are even lighter in weight which means they kick harder.