The buses in Edinburgh are reasonably priced and the service very good. I wouldn't bother taking a car in to Edinburgh city centre, the traffic is bad, parking is difficult and expensive. I suggest park & ride.

http://www.edinburgh.gov.uk/info/200..._park_and_ride

For getting to the parts of the highlands that the buses don't get to (the best bits!), I'd drive. The roads are generally quiet and you have the freedom to stop off wherever and whenever you like.