Best way to get in/around DC if I'm staying in Chantilly?

I'm staying at a hotel in Chantilly, VA, close to Dulles Airport, and I'm just wondering what's the best/easiest way to get into DC from there? I know there's a bus station that can take us to a metro station in Vienna? Or would it be easier for me just to rent a car, since I'm staying out of town? I only really got the out of town hotel because I got it at a great price on it. Any advice would be helpful!!