You're probably joking, but you have spent more time overall in slow queues than you did in fast queues... This is similar to the fact that "your friends have more friends than you do" [0]
My rubric for picking the quickest queue is the one with the lowest total age.
A queue of pensioners will take longer to pack bags, find the right payment card, redeem vouchers and chat with the cashier.
Also tourists and people with many products in their vicinity. Suddenly I really want to collect numbers of this. What's the proportion of age to product count, for example? How many tourists are one pensioner?