In the US, it is always with the traffic.
A bicycle has exactly the same rights and responsibilities to obey traffic laws as a car. If you are in any sort of shape, you aren't exactly standing still relative to traffic, especially in town. In the thick of my city, most serious bicyclists keep up and even beat the traffic because they get to the front at each traffic light, or traffic jam.
Many other run right through traffic lights and all stop signs too. Don't think I would recommend that, though.
But as someone more likely to be walking if I'm not on motor scooter (don't call it a "moped"!). I find bicyclists using sidewalks pretty objectionable. It's also illegal, even if the police rarely enforce it. Most bicyclists I know are of the anarchist rather than the Lycra persuasion, and their philosophy is that we are supposed to be reclaiming the streets from the cars, and leaving the sidewalks for walking.