I would like to eventually try hub dynamo powered lighting, but right now I'm still using my bike's original wheels, so I lack the hub generator.

The first think I noticed when I got back into cycling in 2009 was that flashlights costed half or less of what dedicated bike lights cost. So I bought some some Surefire 6P hosts and some LED drop-ins to try. I've tried many different combinations of Cree XR-E, MC-E, XP-G, and XM-L emitters, as well as some others. The setups I've used have varied from about 100 lumens to about 1000 (actual, not claimed) lumens.

I've learned a lot along the way.

Beam profile is far more important than brightness. My current light is about 100 lumens, and works better than any of the brighter setups that I've tried, because it puts the light where I need it and not where I don't.

The right beam profile varies with typical cycling speeds. The faster one's typical cruising speed, the more throw required and the less spill desired. For slow cyclists, more spill and less throw is required.

Personally, I like to be able to see about ten seconds ahead. I don't need my path lit up like daylight that far out, but if there are large obstacles, I want to see them. I want enough warning to be able to plan and act accordingly (at a relaxed pace) instead of just react. If I can do that at a relaxed pace at typical cruising speeds, then I have a safety cushion for faster sprints and downhills.

I don't like to illuminate an area wider than I can reasonably ride into, assuming the way is clear, at speed i.e., if it isn't an out, I don't want to waste battery power lighting it up.

Because the optimal beam profile depends so much on speed, I find it impossible to make a credible recommendation to anyone without knowing about how they ride. The same light I might recommend highly to one rider I might warn another rider against.

Although it has little to do with functionality or safety, I recommend using a light that emits a tint that the user finds pleasant to look at. Personally, I don't like cool white tints, so I don't want to have to follow cool white tinted beam for 2-4 hours at a time.

Whenever possible, single cell lights are preferable to multi-cell lights, since they allow a little bit more energy in the same volume. (This doesn't apply if an external battery pack is being used.) Especially for single celled lights, hosts that accept 18 mm cells are preferable to those that only accept 17 mm cells. In addition to the increased cell volume, the latest, greatest battery chemistries tend to be available in 18650 (The first 2 digits represent cell diameter in millimeters, the next two represent cell length) cells first.

Buy quality rechargeable cells (and a good quality charger). This is especially important for multi-cell flashlights. In my experience, cheap cells, such as Ultrafire or Trustfire, do not last for as many years or charging cycles as higher quality cells, such as AW. My last battery bill for my bike lights was about $100, but those cells will save me about $100 each month for 3 years or more, since I will no longer need to purchase primary cells for any night rides under about 5 hours (about half that in cold winter temperatures).