At FedEx how it works is the computer decides which truck is best suited for the load. The people who do the intake have to put in so much info, it doesn't have to be accurate info but enough for the computer to route the load (a lot of times the weight is off, sometimes all the info is off, it all depends on how much the person wants to push the customer). Then if it has some special requirement, like refrigeration load or special handling, it gets flagged and goes to one of the trucks that is qualified for it. Outside of that it takes the size of the truck, the capacity of the truck, who has the time and who is the closest - which the last one doesn't always matter.
Most of the time the system works and it is a good system but with anything there are tricks built in that no one sees. Many of the "Dispatchers" have to log their reasons behind changes while others in the place don't. They also pull can loads out of the system to help others out, like getting a WG truck from NJ to Florida to pick up a load in Florida.
Like I said it is a good system.
A $1.11 average, plus FSC, that's d*mn low. What happened?
Size recommandation is the D unit, the bigger the better. Do not make a determination of what truck to get by the company you intend to drive for, always look at it as the truck is a tool and you dont want to limit yourself with your tools.