The hardest is going to find one that does not have all those annoying flashing modes you have to cycle through each time you turn it on. I don't know why that's so popular.
That drives me nuts, I have never been able to figure that out either, unless the Chinese take the name "flashlight" literally?
Does anyone actually use those flash modes? Ever? I have not even once on any light I've owned, it's just a nuisance.
It is used on high power lights (often called "tachlights") as stun/blind mode (self-defense). Though that's a rapid flash, if it's a slow flash then it's a warning mode (neither of which have any buisiness in a low power handheld or headlamp, meaning repurposed crap from Shenzen).