If you're in the front of the line at the store, and a new cashier opens a line close by, should you have "dibs" because you're next in line, or should the privilege be for whoever is quickest to get there?

this question is not because of any particular incident. i was just thinking about it today when i was at the store, waiting in line. sometimes a cashier opens a new line, and calls “next in line.” it seems to be open season for whoever is quickest. should the privilege go to the person next up in the original line, because they were obviously in line for the longest time? or should the privilege go to someone random, maybe someone towards the end of the original line who just happens to be observant, quick and ready? have you ever pondered this?