If you are a small time business owner hiring drivers, I believe by the mile is best. I do flatbed work, and everyone knows the pay in the summer is way better than the winter. If you pay by percentage, drivers will be used to fat checks in the summer. Maybe buy a new car, new house, some toys, or what have you. Then winter rates come. After a month or two, the driver will quit.
Most good drivers are owner operators already. If they aren’t, they like steady paychecks that are dependable.
I would personally pay $0.45 a mile with a $1250 a week guarantee. W2 not 1099, and would pay half of the health insurance. Hometime would be every weekend.