I haven't come across any QS that doesn't have a cashier there (now) but that has changed in the recent past. For a good year, they wouldn't even let you order in person.
That said, there is usually only one register open and the line gets loooong plus you may have to give the door CM a story on why you need to order in person. I'd highly recommend you order on your phone to save lots of time and hassle. You don't have to order it that far ahead. We tend to order 10-15 minutes in advance as we're walking over.