According to everything I could find on this, the more you upgrade your truck, the more efficient they will be. A "good truck" is just a more upgraded or better truck than the one they have currently. Some sources that seem to back this up.
so if you cheap out and give them a lower end truck then they can not work as hard!
After doing some testing with various trucks of different upgrades, it seems any upgrade to the truck increases driver revenue, I'll have to do more testing later but it doesn't seem like the type of upgrade matters, just how it affects the trucks stats/cost.