The only effective lights are the ones you are going to want to use every ride, all the time. Your decision process should include consideration of power source options (rechargeable batteries, USB charger, dyno hub, etc.) and how easy or difficult the process for keeping things in working order is. For me, I prefer to run two taillights - one on blink and one on steady. I prefer using rechargeable AAA batteries and rotating two sets using a charger at my desk. I currently run a PDW Radbot 1000 and a PDW Danger Zone - both use AAA's. I like the Radbot better for it's Philips-head screw case and for its built-in passive reflector. The DZ has a snapcase that is quicker for changing batteries, but a little trickier. I like the DZ for my steady light because it has two red LED's and is thus about twice the surface area of the Radbot, which is brighter but smaller (and which is super for flash mode).