Between Costco/Target/Winco/Walmart/Home Depot/Lowes/Kroger/Uniqlo, my experience is that I can check out quicker than before. I rarely have to wait for assistance, which itself is rarely needed.

I greatly prefer the single queue in self checkouts rather than betting on which cash register line will get stuck on someone that has a pricing issue or something. Obviously, this has nothing to do with self checkouts, but I find single queues far more ubiquitous after self checkouts came around than before.

For lots of stuff, a cashier is probably quicker. But I almost never have lots of stuff.