Depends. Different strokes for different folks, etc., etc.

I live in the Chicago area and night riding goes along with daylight changes, so Night riding is a 2 month or so dedicated activity and opportunistic the rest of the year. I ride road all year long and every Tuesday and Thursday night with a group. In the Fall when daylight gets too short (mid-September) for after work rides, we switch to paved trail, mix of road and trail and dedicated trail on cyclocross bikes. By early October, it's usually getting cold enough at night that a 2 hour ride after work is all that is practical. Depending on how fast Winter is approaching, we'll keep this up until mid- to late-November.

I started out several years ago with flashlights (Fenix L2D), moved up to cheap dedicated light (NR Sol) then graduated to a good dedicated bar light (BD Strykr) and now I'm back to flashlights. I've become a collector of them and like cehoward, I'm always looking for the perfect new light. Their flexibility and diversity means I have several lights for any type of riding and have spares to loan out for any ride. For early Spring and late Summer, I take one flashlight along on road rides for those times when we stretch the ride window into dusk/dark. On a warm night with limited daylight, this can go into a 1/2 hour or so after dark. In the Fall, two flashlights on the bars (1 Flood, 1 Throw), maybe another on the helmet and a couple of spare cells works just fine. I generally have at least one but more often two blinkies for the rear.

With advances in batteries and leds, I have 7-8 18650 torches that are perfect for my style of riding. My favorite is a relatively new player: 26650 Shadow JM07. This format is perfect for me. Bright, compact size and long run time. New models and new batteries coming out all the time. And they fit just fine on the bar with a Lockblock.