Charlotte posted something very sensible about different lights suiting different circumstances (e.g. group riding, urban vs rural). Hopefully she'll repeat it ... !
Is there any need to now?
Given that I ride a variety of different bikes in a variety of different conditions, I tend to use a variety of different lights. One size doesn't fit all exactly and whilst I'll be happy pootling home from town after a night out in the summer with a little blinky LED front and rear, I'd want to pack Solidlights for an overnight audax in the middle of nowhere.
Commuting's when it gets a bit more desperate though. If I'm going to have a prang, it's on my commute, so naturally I want to give myself every chance that I can of being seen and having my speed judged accurately.
I don't have any really dark patches on my commute so I don't need lighting to see, I need it to be seen. Big difference.
I don't like reflective stuff for my every day riding, I want bright, noticeable active lights. This usually means flashing lights. But they're crap for judging distance, so that means doubling up with a steady light. No bad thing from the POV of redundancy anyway.
On my commuter, I have a Fantom BLT on eye-searing flash mode. It's angled a couple of degrees below horizontal, so if a driver gets too close, it'll scorch his retinas. There's also a Smart Superflash in steady mode so those further out can judge distance.
On the front, I have an IQ Fly as my steady light. Often as not, this will be joined by either a Hope 1 or a Fenix L2D on flashy. The Fenix is particularly offensive on flashing mode and you'd have to be utterly blind not to notice it. I only use it like that in built-up areas where I'm in danger of people pulling out on me and I don't aim it upwards on purpose.
If it dazzles anyone that's tough. I'm more worried about being seen than being polite.