Frontlight
I use a front light that I can connect via action camera connection below my computer mount. I would recommend to have a broad front light. In really dark situations like in forests or farm roads you quickly run into the problem that you cannot see the turns. A broader light teppich helps a lot to navigate easily even in pitch black nights. Also I really like the functionality of having a distance light and a down beam.
My personal choice in the Lupine Mini Max SL
Broad front light plus helmet light at pitch-black night. That works!!!
Broad front light plus helmet camera deeply in forest no moonshine…
Narrow front light. Even with some remaining daylight the fall off left and right is strong. At night and some speed it will get difficult to see turns.
Backlight
I think the technicalities on the backlight are not as important as on the front. Long battery life should be granted (as you would not recognize that your light is off). I personally usually mount 2 or three backlights if I am biking in the dark. I figured that car drivers are sometimes really surprised to meet a cyclist on the open road late at night. Also some reflective gear gives my additional peace of mind to be visible for overtaking vehicles.
Helmet light
With a helmet light one clearly looks a bit nerdy - I agree. However, in the pitch dark and especially off road I highly appreciate the possibility to put light in a direction independent from the direction of the frontwheel.