Thankfully there's no need to choose.

Reflectors are indeed pretty awesome sources of light for almost no weight and almost no money. Trouble is that they work well 95% of the time which means they fail for 1 out of 20 cars you encounter. Put in those terms, even a light source that works 99.99% of the time isn't good enough, because it means you're likely to get hit every few years on the road.

IMO in this era of distracted driving, you need to be lit in such a way that a driver who is traveling at 60 MPH and is only really looking at the road once every 10 seconds is still going to notice you in time to decide that maybe they'd better actually pay attention to their driving until they get past you. As such I want to be HIGHLY visible to any driver back to at least 300 to 400 yards back regardless of the situation, and that includes on curves and hills. Reflectors just don't work very well on curves and hills.

Personally I would not ride without BOTH. I have a fair amount of reflective tape, wear a very bright vest when at night (and bright yellow at all times), and I have two daytime-visible taillights that run day and night and two bright headlights for evening/night seeing.