To me there is no riding that's better than riding a road bike on hilly, traffic-free, scenic roads. In second place is track racing, which nowadays is the only time I ride a fixed-gear.
My commuter bike started off as a fixed-gear, then became a brakeless fixed-gear and is now a single speed. It's set up so it's comfortable for short rides around the city and not much else (I shudder even thinking about taking it on a long ride in its current setup).