It depends on what you are going to do when you get there. If you have folks who will provide transportation then fly. Long car rides are a pain in the a$$. Unless of course you have an awesome SUV and are traveling with someone you really want to spend some time with in close quarters.
It depends on how far you are driving. More likely it is going to be cheaper, but you have to consider that the car is using not only gas, but also tires and oil. Every part of the car is being used, which also adds cost to the driving experience.
Flights from almost every major city to another major city are priced so that the cheapest available ticket is cheaper than flying or driving from a smaller town within a metro area. However, you don't give enough detail for us to tell you exactly which would be cheaper.