I used front and back strobes, namely because there are so many lights on the streets - from cars, motorcycles, mopeds, bicycles, even joggers these days - that I think it differentiates my mountain bike from the rest of the traffic. I guess because only bicycles, maybe a few joggers, use strobes. I even use them in daylight and definitely in low visibility (e.g., fog). SK
How about a combination of both? I load my bike up with flashing and constant lights when I'm going to be on the road after dark. Spinning lights on both tires to outline my dimensions to motorists, headlights, brake lights, lights on the pedals... Some friends followed me home from work one night (about 1:00 am) and said I looked like a UFO coming in for a landing. But so far, nobody has ever hit me while biking at night!