I always choose self service because that's where the volume is. I can wait in one of any Costco lines with 4 carts and 1 person checking them through, or I can wait in the line with 4 carts and 6 self service checkouts.

Despite the math working out insanely well for self service checkout, sometimes the gamble still doesn't pay off and the single employee burns through 4 carts faster than 6 self service checkout kiosks.

Costco does pretty good here though, drug stores go slow as hell.

I have a mental list of who the fast/slow checkout people are at my store, would be curious to see numbers but I think the fast people are more than 2x as fast as the slower ones.

I really appreciate the ability at Costco to scan with my phone as we pick up items. Check out becomes a breeze. But I absolutely hate self-checkout grocery stores unless I just have a few items. The idea that I'll run a cart full of groceries through self-checkout is insane. Not only do they routinely not have accurate bar codes requiring some sort of lookup from an attendant. I'll have things which require human clerks to "approve" anyway like wine. In addition, my self-checkout lines don't have the full conveyors like the human checkout lines. So everything has to be moved from cart directly to bag and there isn't enough bag space so you have to start putting bags into the cart which still has groceries. The whole thing is a mess and I hate it.