I think my Rayovac 2 AA indestructible is my current most reliable light due to its thick wall, rubber head and tail. Haven’t really abuse it yet.
What’s your most reliable light if you were to go cave exploring.
No headlamp or spare lights allow.
Zebralight SC62.
Tried and true, never blue, Tekna Splash-Lite. 
Just by virtue of being ruggedised, my Xeno ES1s and E03s.
Also, my simple yet pretty rugged ’502.
YLP Unicorn 1.0 and ZebraLight SC63w.
Any of the many EDC lights that I created by modding cheap hosts. I learned over the years how to make them right, with good components and well assembled, while fixing the flaws that some of these hosts have. They work and keep working.
My current EDC is an exception, I have not modded it because it is almost right: an Emisar D4V2 (post-mugglemodeproblem edition). I have not touched everything inside so I can not trust it completely (I would not trust a Zebralight either if I have not completely disassembled it and build up again) but the build quality looks very good, and the important flaws of V1 are repaired.
I recently picked up a used HDS Rotary. I haven’t abused it, but my assumption is that it will survive more abuse than any other light I have.
I hope so, they are not cheap…
Acebeam L16
two lights that seem to take a beating and not fail for me, which includes handing them to other people to mess with are the, Convoy s2+ and the Jetbeam jet-1 MK.
I have an old thrunite tn-12 that I don’t love. So that is the light I abuse and lend out to others. Has survived a lot of hits, grinds, drops, water, oil.
After all that, still no love for the little guy?
‘Most reliable’ is pretty hard to define, when actual failures seem to be quite rare. I’ve carried an old 4Sevens Preon 2 in my shirt pocket for years, and used it plenty without as much as a hiccup. The more eye-pleasing IYP365 that I currently carry has also been trouble free.
I’ve bashed several ‘S’ and ‘M’ series Convoys around for a long time, and they’ve all hung in there - the M2 in particular is built like a tank.
I can honestly say the only light that’s actually given trouble in the past decade was an early Olight S30 that they promptly replaced, and it didn’t actually ‘fail’ as much as the UI became somewhat unpredictable. The replacement has been great (after I upgraded the emitter to something neutral).
Everything considered, most modern lights are very reliable - but I still always carry at least two!
Malkoff MD2.
Mine is a triple Nichia 219b Convoy S2+ in grey. There are some issues with flicker, but with clean threads it works well.
Haha, I know I should. It’s just to long for EDC and the ui is perfect for muggles, but not for me.
I use my Acebeam X80-GT every day to walk my dog for the last 7 months and never failed so far.
Love the light.
I dont have any unreliable lights… maybe Im doing something wrong.
I dont use them underwater, I dont use them in sand, and I dont do drywalling with them.
I guess Im not hard on my lights at all. I almost never drop one, and Ive never had one stop working when I did drop it.
I did get rid of my 10180 lights, I found they were problematic, flicker, failure to access the low mode on some… so I avoid those, and lights with similar 2 mode pressure switches.
Ive had unreliable Novatacs, but I fixed those with new signal springs.
Ive had a maratac twisty become unreliable when I over oiled the threads, but thats fixed too…
Ive done more damage modding lights, than using them 
but so far all my modding failures have been repaired.
I rely on my magnetic rotaries, and on my eSwitch Tool. I have a dozen AAA twisties, they all work, and I have half a dozen magnetic rotaries, that all do what I expect them to.
You guys have unreliable lights? Why?
I’ve been buying quality lights based on BFL and CPF and the old (flashlightreviews?) for so many years (15 or 20?), that all of my lights are dependable.
My CMG Infinity and Lightwave flashlights are still dependable.
The Sun and the Moon have currently been my most reliable lights, except for the intermittent clouds. All of my battery powered ones are flawless. 