I have done the parks both ways, all car and all bus. The bus was a definite plus for MK. I would not drive to MK again. The other parks are about equal in distance. However, I agree with those who say sometimes the H/P spots close by are taken and the lifting of the ECV can get tiring(Although it is easy to disassemble). Another plus is having a cool bus to ride back to the resort and not a hot car! JMHO.
Have a great trip.