As an American living in Hong Kong:

Cash can be faster because you do know the total before hand since the price on the menu/price tag is what you pay. This is because there is no sales tax or tipping. Buying 3 items at HK$12 each? Your total is HK$36. If there's a queue I usually have my exact change ready before I'm to the front.

In the US, you can rarely tell how much you'll pay since sales tax varies by county or sometimes by city.

A side effect of this is weird totals like $23.76 that result in lots of hard to spend small change which also disincentivizes cash use.