I think CostCo's self-checkouts are best designed/staffed. Other than not accepting cash, they are my favorite (even though still verify scanning of each item, verified by bag-area weighing).

WalMart has two popular designs within my city (not sure if one is just un-updated, yet¿) — their type which accepts half dollars is my favorite cash design.

I have seen designs which don't weigh each item, allowing simultaneous scanning... that also call an attendant to verify if it thinks you snuck an item by (then plays a loop/clip of its alleged violation).

Personally, I have a family member that works as attendant to a dozen self-checkouts... and it seems like it would make more corporate sense to have more human checkers and only allow cash with them.