Ive done this business both ways,% of load,as I prefer,and mileage.What I've found,usually if your on a mileage contract,the carriers dont like to give you empty miles,or very many of them,so you find yourself sitting.On percentage,some companies will pay you a pittance to dead head,some dont pay at all,but the percentage of the load you just delivered,is usally high enough,you dont need to get paid dead head.Now with that said,all the companies have their discounted customers,and on perentage this could hurt your revenue,but,deals are made every day.Back up loads get pre-dispatched,that will bring your revenue up.It's your choice,before you sign a contract with mileage pay,find out what kind of miles the other trucks your size are running.then you can make your decission.