If you're doing it for exercise, a stationary bike makes far more sense. You can do it in the comfort of your own home, more carefully monitor your heart rate, resistance levels, calorie burn, etc. and not have to worry about exhaust fumes, road rash, punctured tires, stop signs, intersections, stop lights etc. In short, in an hour on a stationary bike and an hour on a road bike, you'll get better quality exercise on a stationary bike.
If you're using a bike for commuting or general transportation, a car is far more useful. You get where you're going faster, can carry more stuff with you, and you're not sweating like a hog when you get there. Some people will argue that in a big city they are more efficient (i.e. the bike couriers in NYC), but in all honesty, the only advantage they offer is that it's far easie to flagrantly violate traffic laws on a bicycle.
In my mind, the only place a bike really makes any sense is if you're taking a mountain bike someplace you really can't get in a car.
“In my mind, the only place AN ATV really makes any sense is if you’re taking AN ATV someplace you really can’t get in a car.
There, fixed it for you.