For EDC I prefer a handheld light but for a BOB or working on something it's headlamps only, and with BOB lights it's a single CR123.

Single cell lights are more reliable since there are fewer cells to fail (and failures don't cause reversed polarity anywhere).

CR123 batteries can have extremely long shelf life, longer than me anyway. A CR123 light that has been tested will probably be ready for the rest of my life.

Regulated lights are nice as they don't fade towards the end of battery drain but you do pay a price in total light per battery, and a big price in overall usable runtime. The old Luxeon 1w emitter could produce enough light to walk a dark trail for *30 days* (!) continuous run-time in a Maglight 3xD body. That combo was my ideal hurricane last-stand light but I'm not sure anyone makes direct-drive D-cell lights any more.

Lumens, tint, etc - these were often done poorly until recently. But today it's really a question of runtime and battery choice unless you want extremely long range.

Where flashlight designers earn their money today is in thermal management: LEDs can't take much heat and once output gets to 200 lumens or so I start looking at heat dissipation before handing over my money.