Trail riding? You'll probably want a helmet light, too, so you can see around turns.
I have a Dinotte 200L on the bars for road riding. If I want to go faster, I add a Fenix flashlight on my helmet, since it's beam is narrower and projects farther. I can see where I'm turning onto a side street, and can light up potholes or other problems ahead on the road.
I like the AA rechargeables. They are cheap, and I can replace them when they don't hold a charge as long. The Fenix uses them, too.
The dinotte o-ring mounting works very well on my bars.