Any that are text/TUI/"green-screen"-based are often lauded for speed once you are familiar with them, so there is that kind of best. And if they are still in use even today, then that survival is a strong point in favor of them being "the best".

As far as specific products, NCR Counterpoint is one that stands out amongst those I have used. Fast and flexible, kind of easy to figure out most things on your own.

The Costco cafeteria self-service kiosk seems to be an amazing POS (customer perspective). Incredibly optimized in every regard. The receipt seems to print out before you have even finished removing your card from the chip reader.

Anecdotally (in Australia), as a customer I found the square readers [1] linked to ipads were the smoothest and quickest. And I use a mix of cards - credit, prepaid gift cards, debit.

[1] Probably this thing: https://squareup.com/shop/hardware/au/en/products/chip-credi...