I prefer dedicated bike lights with separate rechargeable standard-size batteries for a number of reasons:
- A spare set can be carried so you're not screwed if you run out of charge
- The unit isn't dead if the battery fails
- No need to remove the unit / locate it near the charging method
- No need for a separate USB charger (didn't have any other compatable devices at the time of purchase)
Unfortunately units of this type seem to be increasingly hard to find; replaced by usb-charged alternatives with propriatory internal batteries.
For the rear I have a Moon Pulsar; a nicely designed and versatile little unit that takes two AAA's:
For the front I either have a dynamo driven unit on the town bike or an LED Lenser headtorch (with 3x rechargeable AAA batteries). I carry three spares so I can replace the batteries in one unit should they die while out
