Wood et al. (2009): Drivers’ and cyclists’ experiences of sharing the road: incidents, attitudes and perceptions of visibility. Accident Analysis and Prevention, 41 (4), pp. 772-776
About differences in the visibility as perceived by bikers and drivers:
The largest difference relates to the visibility of cyclists using lights on their bicycles, where cyclists rate themselves as significantly more visible
when using bicycle lights than did the drivers. This difference, in turn, is much greater at night than during the day.
Flashing lights on wrists/ankles 4.03 (0.96) 4.23 (0.84)
Bicycle lights 3.3 (1.15) 4.5 (0.67)
Visibilty on scale 1 to 5; parentheses: standard deviation.
So cyclists think they are both equivalent, with a possible small advantage for the steady light, while drivers thought the flashing lights to be more visible (but remember differences between detection and recognition, see below) to be better, but still less visible than the bikers thought the flashing light.
With regard to the distance:
An analysis was also performed with regard to the average distance at which
drivers and cyclists believed that a cyclist would be visible to a driver using low-beam headlamps at night. On average, cyclists believed themselves to be visible from 110.3 metres (sd = 157.662), while drivers believed a cyclist would only be visible at 48.3 metres (sd = 58.69) on average
(that is, at less than half the distance estimated by the
cyclists), t (1424) = - 9.247, p < .001.
Probably even more important than deciding whether flash or steady light is better, is actually using the light:
While the use of visibility aids was advocated by cyclists, this was not reflected in self-reported wearing patterns
Maybe this Cochrane review: Interventions for increasing pedestrian and cyclist visibility for the prevention of death and injuries is useful for background info, and they have a few comparisons of steady light vs. reflector and blinking light vs. reflector:
Blomberg 1986: A flashing light held by a pedestrian yielded a greater detecti
on and recognition distance when compared with reflectorised accessories
(420m versus 207m and 96m versus 92m respectively).
Watts 1984b: A rear bicycle lamp yielded a greater detection distance when compared with reflectors (306m versus 184m).
Watts 1984c: A flashing beacon on a bicycle yielded a greater detection but not
recognition distance when compared with reflectors (588m versus
444m and 59m versus 71m respectively)
It also has a lot of comparisons of reflectors on moving parts vs. "static" parts: "biomotion" configurations are better detected.
Personally, I have steady lights both in front and rear (Germany), but I have an additional rear light that I switch to blinking when I judge the conditions particularly dangerous.
I've heard that rather than the absolute brightness of the light, the lighting area is important for visibility. Thus, lights with larger reflectors (the inner mirror) are probably better for visibility. Which is contrary to the current trend to smaller reflectors and LEDs which are brilliant, but basically point sources.
However, I could not find the study.