If someone already has a car, it would probably make sense to drive to Universal because the only extra cost is the parking fee (which I think is $14). But, if you are only renting a car for that day, that would cost another $40 or so, making the total cost about the same as 3 people taking the shuttle. Driving an unfamiliar car on busy, unfamiliar roads can be kind of stressful, so it can be more relaxing to take the bus. You give up the freedom to come and go whenever you want, but there is some value in leaving the driving to someone else.