I have had several light setups over the past 15+ years of night riding. Currently, I'm riding with two NiteRider Lumina 750's on the handlebar, and one Serfas USL-505 on the helmet. I also have a Serfas TSL-750 that I can supplement on either the bars or the helmet. These are all self-contained internal battery type lights.
There are plusses and minuses for all lights. It's a matter of getting the one that works best for you. I had external battery type lights for many years, and it seemed like there were many problems related to the wiring, and I was constantly making repairs. And I didn't love having to strap a battery somewhere and then route the wires. Just not appealing to me.
The lights I have are primarily (I imagine) designed for commuting as evidenced by their relatively narrow beam pattern, hence the reason I have two on the handlebar so they make one rectangular beam. I prefer the Niteriders for the handlebar for a couple reasons: 1) The gradient of the beam is considerably less . . . . harsh than that of the Serfas lights, and 2) the handlebar mount on the NiteRiders is much more solid. the Serfas handlebar mount can shake like a wet dog when railing rocky, rough trails while NiteRiders are much more stable. I like the redundant aspect of having two separate lights on the handlebar. If one goes out, you still have one to get home with. I have been caught out with a malfunctioning light, and it's either a slow ride, or a long hike when your only light fails.
I like a flood-ish beam for the handlebar light, and more of a spot-ish type beam for the helmet light to shine wherever I may be looking.
For the helmet, I like the Serfas lights. Since I usually position the helmet light further up the trail, the harsh gradient isn't so noticeable. In fact, the more concentrated beam of the Serfas will reach out further than the NiteRiders that have a similar Lumen rating. I also prefer the Serfas helmet mount over the helmet mount of the NiteRider.
The USL-505 doesn't have the reach of the TSL-750, but it is bright enough for most conditions, and much lighter, which is important in a helmet light.