There's a pretty sizeable & vocal contingent of cycling activists who will tell you that an oncoming driver's depth perception is less accurate when fixating on a flashing light; it's much easier for cars to judge their distance from you when your light is always on, not blinking.

For this reason, I try to use a combination of steady & blinking lights: Blinking so I can be "irritatingly" visible, and steady so they can figure out how far they are from the irritatingly visible guy and not run him over.