Greyhound bus across the US

A couple of my friends and I are going to be tripping across the States, east side to west side. We're still deciding whether to hire a car and make our own way across or to take the Greyhound bus. Everyone says the greyhound is an institution and is an experience in itself, but a car could give us more freedom. And shared between 3 people, wouldn't cost much more than the bus.

Advice?