"Best light" is sort of like "what bike"- it depends on your comfort level, budget, speed, terrain, environment. Some people make do with a 200 lumen light to see by, while others think that the 200 lumens would be a good 'be seen' light.

I tried running a cheap (or most powerful 3xAAA Coleman) flashlight in conjunction with a Zefal bike specific light. The combo put out just enough to see by at walking speeds for me. Finally upgraded to a 18650 flashlight rated at 510 lumens. There is enough for me to see by in my neighborhood on the Medium mode; I run it on High when on streets I'm not that familiar with or there is more traffic about.